My guy is about 8 months old. I've been feeding him a hopper mouse a week, and he's 22" and 220g. He looks quite healthy. His body has a very slight triangular shape, and his skin is good and tight. He's active, and everything is clear. Two sheds since I got him 5 months ago, and he's grown quite nicely.
Once I run out of the F/T hoppers (which are the same diameter as the widest part of his body now,) I'll change foods. I've got 8 mice left.
Should I get adult mice, or weanling rats? He seems to be doing quite well on mice, but I've heard rats are more nutritious.