How often have you weighed him, have you noticed any weight gain/loss? That sounds like a reasonable weight. I don't have any young pythons for a weight comparison.
Snakes do get some folds in their skin when they turn around tightly (in a rather understated kinda way), but if it's more wrinkly it might be that the skin is a bit loose. Indicating dehydration, or being underweight, or being close to a shed. The most likely of these is shedding. You might have missed his eyes going cloudy, it's not hard to miss.
Since you're here, what do you feed him? I personally go with approx 15% of his weight fortnightly for growing snakes. It's pretty common to get young 'uns a little underfed, people don't realise just how much they can eat.