I don't think that you can be "too old for Gaia." Maybe some threads might be more or less welcoming for someone of your age group, but I don't think you should have to leave because you aren't the average age.
I'm a college student and know plenty of other fun-loving college students here. I don't see any reason why we cannot continue to fit in here for years to come.
Now, if your interests change as you get older, that's another thing, but "too old for Gaia?" The idea just seems ridiculous to me.