what happens when you can't keep up with the group?

It depends on "where" the strenuous segments are.

On the Best of Ireland tour I think the most strenuous day was the day the group went to Carrick-a-rede bridge. I have a fear of heights so I waited at the cafe for the group to return. The Giant's Causeway part was pretty much on your own so you could do as much or as little as you wanted. The tour itinerary lists Day 3 as strenuous but that was spread out over the day so didn't seem like a lot. Day 4 we toured the fort together and then walked back to town on our own so everyone did it in their own time.

On the Best of Scotland tour I think the most strenuous day was the day in Edinburgh with a walking tour and then Edinburgh Castle. The tour itinerary lists Day 6 as strenuous but we took a boat to Urquhart and then toured on our own so you can add on as you please or take a break.

On one of my early RS trips some were complaining about the pace the guide set and he said "Stay right with me". Don't fall back in the group as you'll never catch up. He was so right about that.

What kind of walking are you doing now? Do you have any stairs or hills in your current walking routine?

I'll be honest, I haven't taken a RS tour, but other tours. I have seen people ignore the pace and fitness requirements, or overestimate their abilities and then complain when they are challenged to keep up. It isn't always easy to know what the definition means, but you need to be honest with yourself what you can do. (Going on a safari in temporary tent camps is going to be hard when you need a cane at home, for example. Saw it. Heard the whines.)
You know for RS you have to be responsible for your own luggage, so pare down to the absolute necessities. Pack it and walk it for a mile around your neighborhood...adding stairs or hills is even better.
Cobblestones are much harder on feet than pavement, and know Edinburgh is hilly.
That being said, in any place you have 2 nights, you can elect to not join the tour that day...just tell the guide. Decide what you don't want to miss and take a taxi to it. Or take a longer break and arrange to meet the group at a time or place. Elect to skip optional activities or meals.
I was on a recent India tour where I was struggling but due to illness. Granted I was 65 and the rest of the tour of 8 people was 24-50, but the guide advised me when something would be a strenuous climb and suggested a cafe they would pick me up at or I would just meet them in the square on the way back. Some activities I chose to miss. That way I didn't hold them up and I could recuperate as I needed.
Generally, there are options and be honest with your guide so they can advise what to skip or modify.

Hi,

We did both of those tours back to back last year (Aug/Sept). The most walking we did was the full day that we had in Glasgow. It was beastly hot and the local guide was trying to keep us in the shade.The itinerary on the last day calls for a walking tour of Edinburgh’s Royal Mile but our guide left us to do that on our own. In Ireland, our first full day was a good bit of walking but you could opt out if you want at any point and go back to the hotel. Just talk to the guide. In Kinsale, we took our tour bus to the fort and walked back but you have the option to take the bus back from there. In Dingle, the tour hotel was lovely but a bit outside of town so you will need to walk into town for one of your group meals. I would suggest skipping the walking tour of Dingle which we did not find interesting at all. In Inishmore you can choose to walk or not to Dun Aengus. We were on our own for that. At the Giant’s Causeway, you walk downhill to the site but then have to walk back but there is a shuttle bus that will take you back for 1 GBP. Our guide encouraged us to walk up the Shepherd’s Steps which was super strenuous and I found it a bit difficult. I would rather have spent more time at the causeway and taken the bus back up. Talk to your guide before any of these activities and let them know your concerns and ask about options if you feel any of these activities are too strenuous.

I haven’t done the Scotland tour but agree with Pam on the Ireland. You do walk a lot on specific days but I don’t remember there ever being a pace that was anything more than done at a stroll pace or anyone ever left behind because they couldn’t keep up. I would advise that if your tour is in August that you make a point of getting out each day now for a moderate walk.

Your other post is about getting a golf tee time. If you can walk a golf course, the RS tour will be no problem.

I've had some issues with keeping up -- even when I was in good shape from walking and the gym. My knees are iffy and I take a medication that keeps my heart rate slow. The doc who prescribed it so many years ago said that if it got too high I'd simply pass out.

I think that some tour descriptions of the strenuous parts underestimate how bad it is and some exaggerate that.

My experience over several RS tours is that a few RS guides paid no attention to the slower folks (including those who were trying to take pictures), some did and adjusted a bit for them. Some didn’t know enough about the way we were going to realize that it was easier than they thought we could do and some the opposite.

One example of the last combo, is the guide who took us up steep, slippery, uneven, muddy steps without a handrail, even though an adjacent and friendlier route would've gotten us all up the hill faster. Another is the one who arranged for me to walk to a taxi stand to take a taxi down a hill. Walking to the taxi and taking the taxi took longer than walking the steps down the hill did for the group. And guess what? The group said there was a handrail! I could've easily gone down with the group.

My biggest annoyance is the tendency to walk really fast, then stop to talk to the group. What happens with that rush stop, rush stop pace is that the fast people are able to rest a bit until the slower ones catch up and the slower ones never are. I suspect that this is because the RS guides have a time schedule to adhere to. Note that no local guide on any of the tours I've been on has done that. They have paced themselves and the group in a way that we could see and learn from them.

I haven't done the Scotland tour, but I was on the Best of Ireland in 14 Days one last summer. The RS tour guide was excellent. She was very knowledgeable about where we were going and how we were getting there. She didn’t do the rush stop, rush stop thing. She warned all of us about what we were going to encounter and gave us options for alternatives. At 76, I think I was the oldest in the group, but I wasn't the only person who opted out of a couple things.

The only thing I opted out of was going to Inishmore (Aran Islands). I hated to miss it, but the weather was miserable. Most of the rest of the group did go and had a good time, but they also came back looking like drowned rats.

I don't how many your "we" includes, but note that it's standard practice to have a "buddy" on RS tours. And that buddy cannot be someone you're traveling with. You're required to keep up with your buddy, most importantly on the bus.

The guide will call "buddy check" before the bus takes off and buddies need to have eye contact and verify that each other is there. That means that if you decide to deviate or opt out of something with your traveling companion you each need to inform your individual buddies.

People will usually either keep up, or opt out of the walking portion of an activity. They might stay in a cafe. I found that I was extremely glad that I brought my walking poles on my last tour (Best of South England). There were times when I shared one of the poles with a tour mate that would have found the rough terrain impossible without them. I was glad for them myself.

Did you give yourself some "rest" time between tours? Touring can be tiring so plan to take a "rest break" and just refresh yourself.

Been to Scotland and Ireland with RS tours. Unless it is a matter of getting from Point A to Point B, you can always opt out of an activity. We did done that once when the footing appeared to be too dicey for my old knees. And on one occasion some of the 20ish folks decided to make it an aerobic test, so we simply went at our own pace and enjoyed an abbreviated excursion.

We have seen the RS tour leader discuss the situation with people who couldn't keep up, and in one case the person chose to opt out of most daily activities, while we were in a city and all the activities required a walk to get to.

I dont think tour leaders are being capricious or contemptuous, just they have a schedule to keep, such as a timed entry at a museum or sight, or a meet up with a local guide, or a lunch restaurant reservation for the group, and so they need to move along. Delaying everyone else because of one slow person is an imposition on the rest of the group, not something to expect accommodation. And yes we've had brisk walking tour leaders. It's hard enough to keep a large group from being caught and spread out at intersections, due to traffic or people who want to stop and shop. Sometimes we saw them tell stragglers where the group would be and they could catch up on their own.

But OP, I expect the tours you're on wont be as strenuous as you think the description it implies. It generally means that there's a lot of ground to cover in that day, and not necessarily that you will be sprinting to keep up.

I don't how many your "we" includes, but note that it's standard practice to have a "buddy" on RS tours. And that buddy cannot be someone you're traveling with. You're required to keep up with your buddy, most importantly on the bus.

Just to be clear, you aren't required to walk or stay with your buddy at all times, just to report their absence when the guide calls for a "buddy check."

Thanks everybody for the great advice.