The top picture is when I first got him, around 8 months ago. He was around a year old then, give or take a few months, and around 2.5 inches shell length. Now he's around 3.5 inches, maybe a little more.
One tip: get them off live food ASAP. All you have to do is not feed them for a few days, and they'll take to frozen thawed shrimp pretty quick. I hesitated for a long time to try and get mine off live fish and he was pretty unhealthy for the first few months I had him. He wasn't very active and wasn't really showing much growth. Since I started him on shrimp he has improved a lot.
Also; be careful how much you handle them. Taming an AST is different than taming a CST. With AST's, more handling isn't always good. You should get them used to being picked up and moved, but don't spend a lot of time holding them or anything. It just irritates them and will make them more aggressive. Plus, being out of the water makes them terribly uncomfortable. And on top of that, an untamed AST (depending on the individual turtle), isn't even that bad. They tend to just sit there with their jaws spread, so as long as you don't get close to those you'll be good. They don't have the long neck like a CST and they don't tend to strike often or claw at you.