I know that I have to be *so* careful with the senior day care suggestion as that seems to conjure up images of bingo and people who are immobile.
My church partners with a senior center, any one 50 or older can participate in the programs and a younger person can be a "guest" along any of their trips. They plan day trips to local attractions as well as national outings. These people are anything but "feeble". Most of them have me beat in the physically fit department and they are ACTIVE ACTIVE ACTIVE canoeing, backpacking, you name it they do it.
So perhaps "activity center" would be a better name for it? I don't know if they are something that is even available nationally but it seemed like the kind of place one might be able to connect with other travelers.
(And I have no doubts that an 82 year old mom could whip my butt with how far/long she could travel around the parks)
Good Luck!
Brenda