You can ride infrequently and still get enjoyment from it, you don't have to practise with a view to improving to benefit. It's not that expensive to keep a bike running if you maintain it properly, know your limits and buy second hand gear. I seriously wouldn't care about age, who cares how old you are, if you're enjoying riding then that's all that matters. Who cares if trials isn't 'unique'/special any more, if you enjoy it then that's the only reason you need to ride. I'm 21, used to ride trials from the age of 13-15, then gave up as non of my friends did it any more, if they hadn't of stopped then I would have continued. I'm hoping to get a bike when I finish Uni (few weeks) and can't wait to get riding again.