Although yours may be a little on the small side for seven months, I wouldn't let it bother you. I think JKCs turtle is at the far opposite end of the growth curve (to his credit). As long as he's eating, healthy, and has good water quality, he should grow. Keep his water temp up around 78 to 80F and feed him every other day. You might try feeding him a little more at each feeding too but not to the point that there's alot of wasted food to trash your tank's water quality. Some people feed in a small separate container. This works really well once the turtle gets use to the routine.