I'm 18w and I'm finding out my babys gender tommorrow! (:
I found mine out around 16 weeks! it also depends if your baby is in the right position. the technitian had to poke my tummy around to move my baby around
How exciting! They might tell you If the baby cooperates. If not, then you will know for sure on your 20 week anatomy scan.
Usually any time after 16 weeks depending on doc mine made me wait until 20