There are pros/cons to river cruising. Yes, generally an older crowd by probably 75-80% of the passengers.
The one river cruise we took (with Tauck) provide the perfect itinerary for us to see several cities/villages that we wanted to see and then to see exactly what we wanted to see within those cities/villages. The travel between places was for the most part done at night, so we would walk up in a lovely new place and enjoy the bulk of the day touring. Tauck arranged a fabulous lunch at a castle, we had a chocolate-making demonstration, tour of a cheese-making facility, etc.
That year was the Floriade in Venlo, and that was high on my list, too. We enjoyed the spring flowers at Keukenhoff (with early admission), but it quickly became crowded, and when it was time to leave, I really could have stayed another 2-4 hours.
Unpack once, enjoy fellow passengers with similar interests...easy, very few logistics to deal with, etc.
The downside of river cruising, regardless of which brand you choose, you can wake up expecting a fabulous view in the morning, but another river ship can be stacked right up next to your window (as in your could reach out and shake hands with people in the next river ship, if they opened their window or door). WHY? Because the docks only have so much room, and as other river ships arrive some have to stack. When you go to leave your river ship for the day, you will walk on ramps from one river ship to the next, thru the lobbies ( which gives you a chance to check out the competition just a bit). This only happened to us once, but it was really weird waking up to a very chatty old river ship filled with people from a foreign continent who had all sorts of laundry hanging in their windows......granted it was colorful and interesting, but not what we expected. So, now you will not be shocked if that happens to you.
Also, in order to fit under every low bridge, river ships are not tall, so you will likely not have really tall airy ceilings in your stateroom.......that I noticed and missed.
I would not hesitate to go on a Tauck river cruise, in fact I came really, really close to booking a Christmas markets trip with them this year, but I decided I really did not want to be traveling in really cold climates along the river. But, unless the itinerary is bang-on-perfect, between a river cruise and a land-based tour with Tauck, I would definitely go with the land-based options to enjoy the variety of truly fabulous hotels they book..........but, that's me. Others like to repeat river cruises, because they do not want to unpack more than once.
I have not personally experienced low river water issues, or really high-water issues, but 3 of our friends (all on separate trips) experienced that with Viking and they were bussed between locations (and I am almost positive, though not 100% positive) their overnights were spent on other stranded river ships at the locations to which they otherwise would have arrived at in their original river ship. Things happen...NO provider can predict or guarantee river levels.
re: the meals with our Tauck river cruise, seems at least 1/3, maybe 1/2 were on land. Also, we had a fabulous Amsterdam excursion on a barge (or whatever they are called) that had just been used for a visit by the president of Turkey the evening or two before. They served some sort of sweets, one that had been made for the visit of a queen, and seems champagne, too. It was a fabulous, incredibly restored vessel. It's that kind of stuff that really sets Tauck apart. They are a step above in my opinion.........so I guess that's why we have traveled with them several times.