I’m a regular at Rush Indoor Skatepark, its 15 mins from my house:
http://www.rushskatepark.co.uk/
I’m 40 and got my first ever BMX middle of last year. I ride at Rush, and also BMX tracks and local outdoor parks. There’s a decent size contingent of people around my age at Rush. But then the youngsters are all sound as, and don’t take the piss out of us old dudes. Well not to our faces anyway.
All I’ll say is its bl88dy brilliant fun, and since getting a BMX my ability on an MTB has improved loads, most notably in the jumping and pumping department. Also I’m generally faster due to pumping more, sprinting out of the saddle and not braking. All stuff worked on at the BMX track.