Hi
Welcome to the board!! :wave:
That is a little on the small side. They are average of 4 inches when born, and grow an average of 2 inches a month, so based on that at 6 months they should be around 16 inches, but they do vary greatly.
How often are you offering crickets? and how many is he eating?
Also what
UVB bulb do you have? - This can be a factor in size, and health (appetite)
Romaine lettuce isn't great for them, it contains a lot of water, and not much nutrients, you can find better things to feed on here:
http://www.beautifuldragons.503xtreme.com/Nutrition.html
6 months is usually old enough to tell the sex, but at 8.5in long, he may be a little small. You can face him outwards on the palm of your hand, GENTLY lift his tail (this can break the tail, so don't push it, when you feel the resistance STOP) you will be able to see one bump, on the tail not the vent, if it is a girl, and two bumps with an hourglass shape in the middle if it is a boy. I think there is an article in the article section on this board, probably a better explaination can be found here!
Hope this helps,
Could you post pics?!?!?...We LOVE pics!! :wink:
Nikki