Was it a screech like whistle or did it carry a recognisable tune? My sister made that mistake with hers, not DNA proven of course, but when I met her bird i told her I believed it was female, after two months she is believing more and more that I'm right. The picture you just posted, looks like a whiteface pearl, and it does look male, do you have DNA on the younger one as well? My female at a very young age didn't do much more than chirp and "hungry cry" I never heard a whistle come out of her till she was about 6 months old, even then it wasn't even a simple tune like wolf whistling, my males on the other hand will sing, mimick, head Bob or as I call it head bang, knock on cages, and both will argue about stepping up, my female won't leave me alone long enough to get the food bowls out. In person I'm pretty good about studying the body language and subtle hints with about a 95% rate of gender identity, based on what I've seen and read about here, I'm guessing you have two males, not all bad unless you are dead set on breeding, but you have a few years before that anyway. Two males can create an inseparable bond just like they will in a male/female pair, even my 3some meeting for the first time went well, cockatiels are very social.
