There is no one age - all tortoises mature at different rates depending on how they're kept. Size is a better indicator, but even then, there are no guarantees. You may be able to tell as early as two or three years (some males will begin to flash that early) but some are visually unclear until 8 or 10. Usually, if you see strong male characteristics, you've got a male (but there are 'male' looking tortoises that lay eggs one day too). Most tortoises look female until they start to mature, so female characteristics don't mean anything on a hatchling.
