We're not entirely sure how old he is. His previous owner had him and his buddy for about six months, and his owner before that (yeah, he's been shuffled around, poor guy) apparently had him for "several" months. I would wager to guess that the first owner bought them from a pet store, so I also don't know how long they were there either. They look to be full grown, but I guess I can't tell for sure.
He didn't do this at all during the first week or so of living here and he's started to do it more and more frequently (so every single day now). *shrug*