well you can sex any lizard at any age by getting a DNA test by a vet and it is 100% sure but it costs some money. with frillies it usually takes a year before you can tell the sex. some one sold me a 1 month one "male" but it turned out to be a female. it is best to wait to be sure. you can tell a male at 1 years old buy looking at the base of the tale if there are two bulges it is a male if you cant tell feel around the area and try to tell if there is any thing there. I do not recommend you try to extract anything because it can hurt it if it is a male. Also the males have large heads and frills compared to the body size. i hope this helps

good luck
Jake