It is pretty easy to identify male stars early on, at about the 2 year mark usually. At that size if it were male, I would expect the tail to be a lot longer.
Looks like a female right now but I would till its a bit bigger to be 100 percent with my answer. To really know a tortoises age you have to know the date it hatched. It could be 2 or it could be 5. Do you know if he is wildcaught or captive bred?