Never was that mentioned. Plus, "human life expectancy" is definitely a wrong bound. Would it be wrong to play a Pokemon game at 90 (above human life expectancy)? No.
I propose we set the range to [0, Death], there is no reason to use a constant as the upper bound.
Assuming that range, then I will agree that any age in the (0, Death) range will be perfectly okay.
If mathematics in secondary school had been based on practical Pokémon-based situations I dare say I would have been better at it! :p
I have been playing since I was nine (when Red/ Blue came out in the UK) and am still playing at twenty-one, as is my other half who is twenty-five this year. Since we've been together we buy opposing versions of the game and help each other complete the Pokédex.
While the fervour of playing through the main storyline is fresh we tend to also watch the anime. We started from the very beginning while we played HG/SS last year, and still have about three quarters of it saved up to get through - my goodness there are a lot of episodes!
We also have a big, cuddly Pikachu who wears a scarf and beret and sits on one of our chairs in the drawing room.
I've said it before and I'll say it again: nerdy love is the best kind :)
Also, when my other half was in school, his best friend's mum used to play his Red version while he was at school, and apparently she still plays now.
So, no, you can never be too old to enjoy such a far-reaching franchise!
xkcd did a comic (which involved playpen balls - hurrah!) which said that once you
become an adult, you get to decide what being an adult means, and I think that's very apt. And why is it acceptable for older people to play card games, or board games, but not video games? One day conventional video games will be as "old school" as card games, after all. The times they are a-changin' ;)