Since this is my first year with the fat tails, I don't know when they become sexually mature. I just shipped a pair of SW banded geckos to someone where the male was only about 3 months old and when I put the female with him before shipping to acclimate them, he actually tried to mate with her. So the short answer is "I don't know" . I think to be safe you'd really have to have a separate set-up for them. One could go in a 5 gallon, and at this size, you could actually divide a 10 gallon for awhile with plexiglass (put the heater in the middle) and keep each on a side.
I keep looking at the ones I still have and I'm pretty sure they're all female, but if you do buy one and I was wrong, I'll swap.
I keep looking at the ones I still have and I'm pretty sure they're all female, but if you do buy one and I was wrong, I'll swap.