I think your big males are just very well cared for. 80g really isn't all that huge for a male these days. We have several non-Giant male breeders who are that weight and aren't at all obese, just big. For the same reason, the females may have just not grown as quickly because of how they were being cared for. They may also just be smaller to start out with. There span of what's a "normal" size for a Leopard gecko varies greatly.
Thats what i thought(with the giant stuff) i was told a giant is 90-110 and a super giant is 110-140 or something. My guys are big i know for there ages but thats because there cared for like family(no racks, hand fed, handled daily, and what not). I suppose i shouldnt compare the 2 little ones to mine since mine are cared for right instead of like money makers. I hope with good feeding and care that they'll grow some! there smaller then my 3 month olds!