My understanding was that you thought he was thirteen when he fought Perfect Cell. Anyway, he'd be a tiny, tiny thirteen year old, were that the case. I personally think that he couldn't be any older than eleven. Piccolo even brings up the fact that he's a scared little boy to Goku when the time comes for Gohan to fight. Time chamber doesn't count, considering no real calendar days passed. (I know you and I talked about this last night but I want everyone else to understand my opinion).
If you think about it, Gohan was no older than five or six when Raditz came. Maybe around six or seven when Vegeta finally showed up and close to eight or nine when they fought Frieza. So, given the time frames and how a bit more time had passed between the battle between Garlic Jr. and the time that Trunks acutally showed up, maybe a year or two had passed. The Android battle went by quick, considering Cell showed up and absorbed them with no complications. I'm stickin' with eleven. ^_^