Senior travelers

Road Scholar has a few tours for those with mobility issues.

Sage Traveling offers tours for people with mobility issues.

You'll find that seniors make up a large percentage of most tours company passengers.

British company https://holiday.saga.co.uk/ is a specialist holiday company for over 50s - escorted tours, ocean and river cruises. Excursions are often graded for ability.

Senior or not, mobility issues or not, the up down slope is still there. You can only deal with it by having a hotel down at the bottom. Or have some sort of transport to not have you walk up and down.
To my knowledge tours geared to seniors do not usually have transport of that type included in the tour.

As treemoss2 said, location, location, location. Book hotels near easy transportation and restaurants. In Varenna, for example, there is a hotel with a good restaurant across from the ferry landing. Yes, you'd still have to climb up and down to see the town center and enjoy the restaurants there, but maybe a single trip to the square would be enough. Unfortunately, there are a lot of beautiful places (and elsewhere) in Italy that are mobility challenging.

Before booking any tour, read reviews and ask questions. Nowadays, it seems "senior" can be anything from 50 to 100+. That covers a huge range of ages, mobility abilities and more. Even on this forum there are very young 70 year olds and very old 50 year olds.

My advice would be to go places where you can find planning support. Using this forum could be Vienna, for instance, as we have a very helpful local. I've done similar for people who have come here to Budapest. But the forum has great support in a number of locations. Do some posts and see what responses you get. As an example, the Buda Castle is at the top of a 300-foot hill ... no, it's not. It's at the end of a bus route. Metros have 45 steps up and down, except for the ones with elevators. And trams have 3 tall steps up, but tge bus that runs tge same route has no steps.

Then there are the pros in the businrss. If someone came to me with old age or mobility issues and the question of where to go, then besides this forum I would send them to the Balkans where I know a trip planner that I suspect would plan around every step up and create the ideal trip from Slovenia, through Croatia and Bosnia and Montenegro down into Albania and maybe for less than a RS tour.

There are always solutions.

We have taken several tours with Gate 1 Travel and one recently with Road Scholar.
They provide information on how active each tour is expected to be.
I have a bad knee and can handle moderate activity with walking about 2 1/2 miles a day (not all at one time) and have managed that well.
I do travel with a foldable walking cane that assists me with walking.

Frank II gave you a couple oftour companies that may meet your needs. However, as some have already pointed out, age and physical ability are not the same thing. Not all seniors are mobility impaired. I've met 80 year olds on hiking trails in the Alps who passed me like I was standing still, and they weren't even breathing hard.

Almost all group tours will publish their activity levels for each of their tours, as well as itinerary descriptions so you can tell in advance if a tour is right for you. Additional research can show you if the topography of various locations would be too much for you. You would want tours labelled as easy, with full porter service and better class hotels included.. Given your concerns, a RS tour, where you must carry your own suitcases, and perhaps climb flights of stairs instead of having an elevator, might put them out of reach for you.

My mother has done a couple of tours with Senior Discovery tours. It is a Canadian company and it lists its mobility etc on the tour. It arranges everyothing including transport to airport from your home, but that may be only from Canadian destinations. She has enjoyed both of them.

You could also have a look at these - https://www.seniordiscoverytours.ca/ . They tend to be longer tours, so the cost is higher. I've never tried them but they appear to be very popular.

Road Scholar's demographic definitely skews older. Their catalog and web site has an activity level rating for each of their tours. The levels cover quite a range.