Frog, when you say you're beginning to get old... I've just read a library book, The Choice by Edith Eger.
She recalled when she was considering going on to get her next qualification, anticipating it would take her six years to complete.
Talking to her college principal she expressed doubt. "...by the time I get to finish school I'll be fifty." The principal smiled and said, "You're going to be fifty, anyhow."
I'm 'older' in actual years but like lots of people still feel young (headwise I'm still about 23). Do you feel your age?
And, mentioning libraries, they're another place you might perhaps consider volunteering. I work in a library where we have volunteers come in for a few hours a week, or when they feel up to it. Some help customers with issuing and returning books, others get on with quietly shelving books so they're around other people but not having to interact with them. One of our volunteers comes in and helps in the work room, behind the scenes.
We're friendly in our library but we respect our volunteer's space and take our lead from them.
Edith had PTSD too. Her book is about resilience (and hope). And I admit I nearly didn't take it out in case it was too much but ended up reading it in two long sittings. It was that compelling.