My guess would be male. Does he have a concaved plastron?
I have a male that looked female for most of the time I had him since his rescue. He was way under sized for how old he was suppose to be. After rehabbing and some time, space and proper food, he has caught up to the size he should be. He, is a male, but not yet with the typical amount of a concaved plastron as my other male and tail not quite as long, but for sure a male.