i got him of garthnfay i got him for free as i gave him a coastal carpet python but the are normaly $85.he said it was 9 months but me and a few of my mates thinks its alot younger
I don't believe Garth and Fay would knowingly feed you false information Jessie, so you can be pretty sure its an accurate account of the turtles age.
As Olive said, they grow quite slowly, grab a book on turtles at your local library, or do a search on the net, you'll find information about them, and it should give you a good idea of the habits of the average Turtle.