Thanks for the Motosouth tip. I did, and it's helped a lot. I'm pretty sure we're going to go with a 250f. Now, where should he go to ride for the first time? East of BR, preferably.
Riding for the first time? You surely don't want to just drop a brand new rider on a 250f, bring him to a MX track and let him have at it. If it's open the Spillway just out of New Orleans would be a good spot. It's fairly flat and the terrain varies to give him a good feel for the bike. If he's never been on a bike there's certain things he needs to learn(on flat ground) before ever setting foot near a track. He'll need to learn how to work a clutch, where the "friction zone" is, how to properly shift and (importantly) WHEN to shift. Things like learning how his tires will react in corners, same with brakes. The first time he grabs too much front brake into a corner the front will wash out and he will indeed eat shite.
With that said 250F's can be a bit of a pain as far as maintence goes and this is something that should not be overlooked. I'm not saying don't get a 250f, I'm saying you should be aware of what you're getting into. A 250f would probably be alot better for him in the long run than a 150f. 250f's generally make alot of their power in the upper RPM range, problem with that is revving a 250f too high, too frequently can cause valve train issues. It's not that big of a deal as long as the bike is well maintained, but just know what you're looking for. You seem to come across alot of 250F's for sale with top end damage because owners lack the mechanical ability to make the proper repairs.