

I already have my male some males develop slower than other males, you may have to wait a few more months to tell for sure.
:
Go into a dark room. Then, lift tail (as you have) and place the small flashlight on what would be the top of the tail (just above the vent). Simultaneously, look at the underside of the tail (&/or take pic/s).
If done right, you should be able to see the hemipenes, just inside the tail base, or the absence of them.
no heat to worry about because a LED key chain light was used