Ok, so what should I be looking for to determine the sex of my sully? I know it is way to early to tell as he/she is a hatchling, but I want to know what to be looking for in the future.
If its a hatchling there's no way to tell or even guess. When it gets older smaller tail means female, larger male. Male sulcatas will also get a large indent on the bottom of their shell and grow much larger than females.
Everything previously stated as well as the anal scutes on a female are typically a horseshoe shape and the males anal scutes are much wider and flaring out. The gular on the male will be much larger that that of a female too although this doesnt show until he gets older. Some males start flashing what they got at an early age so he may show you what he is before anyone even has a clue as to what sex he/she is.