I have been on a couple of river cruises with riviera---age range was more towards 70-80---i'm 56 but I did enjoy meeting people a bit older than myself---most were ---young at heart-- and there were a few folk about the same age as myself
I've just been on one of the Solo Travellers tours and I loved it. I'm 70 and didn't feel that I was an "oldie" in the group. There were a few people who were only in their 30's. Everyone fitted in and age really didn't seem to matter.