A 15.2 palomino, and he's been riding since he was 5, and this is only his second horse!!!!
Firstly if, he'd been riding since he was 5 this would be his 4th or 5th pony, so i'd miss that bit out. A palomino is a bit crass, as palomino is a colour not a breed, a fancy colour at that. Go for something a bit more real, a 15.2 cob cross, a 15.2 grey,etc.
He could be doing one day events, ( show jumping X County and dressarge) point to point, amature racing, hunter trials, sponsored rides, X country events, playing polo, or polo cross, a combination of la cross and polo (great). or dare I say it he could be hunting, drag hunting preferably.
He could be attending pony club senior camp (lots of girls!)
The posibilities are endless.
But not on a palomino mare!!!!!!!!!!!!!!!! get the lad a good believable horse
Good luck with the book