Healthy weight?

I just got a scale and weighed my ball python today, it was 120 grams
.. That seems really light to me but he's only about 4 months. He eats a small mouse every 7 days without a problem, although im gonna him up a size soon, and looks healthy.

Every snake is different on the growth rate although 140g for that age is on the low end. Health is determined by other factors such as muscular composition, alertness, digestion, etc.

Do you know how much he hatched out for? If he hatched out under 50 grams it might explain why he's only 140g now.

I'd switch him up to rat fuzzies or rat pups, feed every 5 days and see how it goes.

That's what im gonna start doing, and no, I don't know D: I thought hell be fine cause he's not having any problems but he my first snake ever so im a noob at this and wanted to make sure he's fine