The tail base. The males have a thicker tail by the vent(where they poop). Also the colors are starting to show of a male also. The males also get a bulge in that area which is their private parts. He doesn't quite have one yet(very slight), but he will as he matures.
Definitely a boy, likely in the 3-4 month range. Would be small for 6 months if that old. As for what kind of panther, no one can tell you for certain, except the place you got it from.
Male ambilobe, looks like the blue bars are going to turn red or possibly a combination red and blue, but I bet they'll turn red. jmho. Here's one of mine that ended up with red bars.