When will I be able to tell the sex of my tortoise?

[JaySparks]

My hermanns tortoise is 10 months old. His tail is thin and long. not stubby like a female.

 

[JoesMum]

My hermanns tortoise is 10 months old. His tail is thin and long. not stubby like a female.

At 10 months you cannot tell. You have a few years to wait, I am afraid.

Gender becomes apparent by size rather than age as size determines sexual maturity

Your tort will need to be around 5 inches (12 cm) SCL before you can have a guess.

When the time comes, post a good clear photo of the underside including the tail and we will help.

How big is your tortoise now? Here is how to measure Straight Carapace Length
http://www.tlady.clara.net/measure.htm

 

[wellington]

If it thin and long you probably do have a male. However, that can't be determined 100% at such a young age. A lot of torts seem to flash around the age of two if they are male. However, that's just by chance.