kyryah said:The reason that they could not tell you his age is that the tortoises that Petco sells are wild caught. (Not telling you an age is actually a step up for them, I have read numerous times where they have told a new owner that their tortoise is 3 months old, when it is obviously several years old.)
It is hard to tell for sure, but based on his size and condition I would hazard a guess of around 5 years old.