Somebody's saying that Tails jumps from about 5-10 (now 11) years old in the comic, after eating from the Tree of Knowledge. I don't remember this age jump... what issue? ...sorry guys, I just don't feel like looking through a decade+ worth of comics right now... ^^;;;
That would be comic issue #14. Tails eats a fruit, the only fruit, from the Tree of Knowledge and becomes smarter. Tails does not jump in age, not exactly. His MENTAL age go up considerably, AKA he gets mentally smarter, and of course creates and tries to execute a plan to take out Robotnik, which of course leads to no end of comedy. His physical appearance and age does not change in the comic, only his smarts. I hope that this helped.
There was a time when they said that the fruit had made Tails age from 5 to 10, both physically and mentally, but this was before they'd decided that it'd been ten years since Robotnik took over. So yeah, what Betheny said - ate the fruit, got smart, went back to being normal albeit maybe a bit more experienced.
Somewhat off-topic, but how much older in years is everybody? Sonic has had like what, 3 birthdays now. (not counting the ones from before the 20's). I'm somewhat confused.
Sonic's had three birthdays in #12 (15), #68 (16), and #160 (17/1 . Everyone else is presumably about the same age, but the "year away" confuses things a bit - I think it's more likely to be about nine months away.