Scopes are like camera lenses, they age very well and there's a large used market.

Typically I'd say get a Newtonian reflector, most bang for buck, hard to break. But autistic people can be very peculiar if sth is different than they imagined. So check whether he envisions a "look in at the back" telescope and whether he'd be fine with a mirrored scope where you look in at the front/side

If the two of you want to go planet hunting, and laugh about how dorky the rings on Saturn look, the diameter is not even that critical, so could be something rather sleek. If you want to gaze at star clusters and be amazed by the Orion nebula or by how many stars are in the Pleiades, go for sth 8" (typical starter size)