Hi mate
If he's only ever flown two channel, I would not go above 2 feet wing span...!
Larger helicopters are gonna do a LOT more damage if you get it wrong. I really would not go above a 450 size this will be plenty for him to get to grips with if he's only flown two channel.
I would recommend a blade 400 or 450 as spares are plentiful and they're easy to repair if he crashes it, which he will! And it is far less likely to put him in hospital
.
Just a thought
rob
Oh, and get him training gear... He WILL thank you