What the heck?!? Gender question!!

I'm about to be 16 weeks and my next appointment will be around 17 weeks....how In the WORLD is everyone finding out the sex of their baby before me and they aren't even as far along.....I haven't had a sonogram since I was 8 weeks...and I'm not scheduled for another one until I'm 20 weeks.....some women have found out at 14,15 and 16 weeks...not gunna lie, I'm kind of jealous!!!!!! Does anyone else not know the sex yet and is having to wait until 20 weeks like me?!?