A demon's ability to affect the world is proportional to the ability of the host to affect the world.
It's not so much puberty itself, as the various restrictions humans put on human children that make it harder for a demon who possessed a child to be able to do things.
If a demon possess a host, they likely want to be incognito for a bit until they fully check their powers are working as intended, and able to do so away from unpossessed humans who might call for authorities to investigate the possession, or to attempt an exorcism themselves.
What's that? This one's host has to be back home by 7:00 p.m.? Given education during the day, that's basically an hour at most to work if they bolt after a 5:30 dinner, which might stand out.
Well, maybe I'll get a drink to help calm my host's nerves and get more power usage out of that - wait, my host can't get a drink at the local bar?
This is very annoying - clearly something must be done about these parental units, but I can't confirm my host is powerful enough to take on these parental units. And it's likely the authorities would investigate us taking them down, so I'd need to get my host to leave and live in a forest, I guess, and potentially buy things with the leftover funds the parental units had.
Wait, my host would get caught trying to use a car and likely pulled over by the authorities?
Well, okay, I'll leave as a result, and live sort of out of town - people won't be suspicious if I keep a low profile, and just eat a lot of forest mushrooms.
Solo children also stand out, and would likely be interrupted by authorities or parental units of other children for being alone and away from others.
Much like these above restrictions, a solo child host can't usually walk around disaster scenes unnoticed, and would likely be picked out by parents or authorities trying to help, even if they're trying to do mischief at a carnival or a major transport location.
At best, this starts to get suspicious, and makes it harder to get away with actual mischief.
You might want to adjust some of these specific rules based on the society in question, but in general - the demons in question have a lot more leeway with what they can do that's demonic if they're older and given more privileges, especially when their host isn't part of a demonic conspiracy through a whole family all in on the possession. And even then, you have societal concerns to worry about
Better to wait for them to have more curfews lifted and more permissions provided and expected, and just work from there.