With current research being done on Melatonin, it's a fact that we naturally produce it, most abundantly when we reach puberty. And on top of that, if you smoke a joint, your levels are gonna go up 4,000%. Melatonin production, being more prevalent in youths, could be the reason why younger users are "slowed down" and affected by Weed more. Again, I don't know what an overdose of Melatonin can do.