Make sure to ask how many battery cycles the battery has done. I bought a 2014 11 inch Air secondhand for uni and the battery was stuffed. I ended up doing a third-party battery replacement myself, but it's just as bad. You don't want your son to be the kid hunting for a power outlet all the time.

For high school? Why not just go the Chromebook route? Not sure what it's like outside Christchurch, but that's what all the kids seem to use down here. Zero admin!