I don't know about TX but here in MA you must be 18 to register and even get a loan with a co-signer meaning you would have to put the car in your name until he hits 18.
$2500 is a good job saving, I would suggest he get something in that range or save up some more. Have you also tried calling around for credit other places? Providing your credit does not totally **** and have a ton of defaults and chargeoffs a $2500 loan should be chump change no matter what balance %'s you are carrying, it may have just been that one place.