The AF doesn't use max allowable weight once you are in. They use appearance, PT test scores, and a BF % system. I don't like the method they use to figure BF though...
I don't know about the enlistment and pre-enlistment rules are anymore.
When I retired a little over a year ago, I weighed nearly 230, at 5'11". On the old max weight chart they used to use, my max allowable weight was about 199.
Even then you could go over the max if you looked OK, had some muscle, and met their BF requirement.