Well, I have never gigged past 55, as I reached 55 in may of last year and we were locked down. But I gigged a lot at 54 and hope to gig a lot at 56.
The audience is whatever, generally speaking 20 - 60, depending on where you are playing. We don't do many 'oldie' things, apart from one place, but it is the general crowd of the night time. We also don't seemed to get booked for many kids paries, although we did a charity thing for a religious school locally (where unfortunately I we connected the drummers mic before mentioning it to him, he has a bit of a potty mouth) - good gig, opened with highway to hell.
I don't see age as that relevant if you are just doing local circuits. Obviously if you want to do young teen pop group you might have missed the boat.