Stephanie,
This looked like a good site with some good advice. See Here:[
www.anapsid.org]
In my experience, if well cared for the turtle should grow fairly rapidly. I used to feed
the terrapins, Melissa and George, and a slider, Clyde, in a kitty litter pan full of water rather than their own tanks after they got larger. Otherwise it creates a terrible mess in the tank itself and that means the gravel has be taken out and washed/cleaned fairly frequently or the odor can get quite bad. (I kept the slider separately, by the way, as he became quite aggressive and kept nipping the male terrapin on the tail. Since this is the housing for the turtle's sexual organ, nipping was definite cause for concern, and did cause a slight infection. Pet stores sell [or did sell] "turtle tetracycline" for such purposes.)
The article tells you to sex turtles by overall size, and by width of tail. This is not particularly useful in very young turtles; the best method I know is to turn the turtle over and look for the cloacal vent: in females, the vent should be within the margin of the carapace, in males, beyond it.
Turtles do not have to hibernate (you probably already know this), and in my view you should not attempt this. Some friends have tried, with varying (but invariably low) degrees of success. You are better off keeping the temperature within the turtle's normal range year-round and continue normal feeding.
That's all I can think of for now, except a slight warning. Male red ears can, as noted, be aggressive; they're much smaller than females, however, and the aggression is pretty ineffectual. Female red ears can grow quite large and reach several pounds. Over time, they can become quite a lot to handle. As I said, I like turtles a lot, but they are most emphatically not carefree pets. Good luck again. Hope all goes well.
Lee