I'm with Brian on this one, 17 to 18 months old is old enough to breed in the wild, and old enough to start breeding in captivity too.
Last season I bred 3 virgin females that were 17 months old and got eggs from them the week they turned 24 months old.
Perfect eggs, perfect babies, and momma snakes went back on feed and all 3 were around 2000 grams before breeding this season.
There's nothing wrong with waiting until the female is 3, sometimes you'll get larger first clutches, but not always.