LMFAO actually I always assumed that in the show his parents guessed his age wrong by a few years because well he couldn't speak English nor know how to interact with other children. I always figured they simply had him start school late having to relearn all the things children normally learn between the ages of 1-4, so when he started kindergarten/first grade instead of being like 6 or something he was really 8 or 9. Hence when Lex meets him Lex thinks he about 18 minimum not the 14/15 year old freshman he's pretending to be.