You're only "too old"
when you start believing you are.
My online experience with Minecraft isn't negative, quite the contrary, the server I play in is pretty well organized and functional, despite the average age of players.
To me it is surprising to see the other players' real age show when I pay attention to their conversations on the chat channel. Suddenly learning that one of the more active mods is a girl whose age I almost triplicate
can be quite a shock.
Maybe a case could be made that the open ended nature of the game results in more player implication, as it is players who design the rules of their interactions with one another, rather than have it defined by a scoreboard or a strict set of goals.