Hi, my butter is around 18 months and he just weighed in at 130g. As long as they get plenty of exercise and have good muscle tone don't worry. A good way I was told to measure muscle tone was this; hold the snake around 2/3 of the way down their body and let them hang, if they can get themselves back up to your hand then they have good muscle tone! If they can't then more treadmill needed! Very handsome boy by the way!