Students are weighed to ensure that they meet the minimum and do not exceed the maximum weight allowable within Naval Aviation. (Minimum allowable weight is 103 lbs
Pretty sure that's just to get you into the T-6 seat, but other seats have higher minimum weight.
For the other anthro measurements, minimum arm length and leg length seem to be the critical ones (gotta reach all the switches and work the pedals). Long thighs will get you kneecapped in an ejection and too tall sitting height is probably what got Nick Bradshaw (RIP), but you gotta be insanely short to not see outside of any of the helicopters with the seat all the way up (including sit on an approved seat pad as the case may be, which are actually a thing). Short thighs don't really matter as much as overall leg length, as long as your feet can reach the pedals.
The 53 and 60 seats and pedals have all kinds of adjustment. The 57 has pedal adjustment only (and extra pads for the seat, but you gotta work see the AMSO for those... and the AMSOs usually seek out the
short people anthro corner cases when a new class of students checks in) but nonetheless a few people with pixie and hobbit builds have made it work over the years (made it work legally I mean).
I can't speak to the P-8 and the King Air seats. I do remember a few of my vertically challenged fellow students getting P-3s.