In many animals, including humans, the young go through a "learning and experimenting" phase in which they're very curious and very open to new ideas. Eventually they leave this phase; they become less interested in learning, and more interested in doing well for themselves with the world as they understand it.
It's difficult to know how much of this phase transition is "hormonal" versus how much is based on the person getting older and simply deciding they have enough experience, but I'd speculate that someone whose body was frozen at a young age would feel more playful and more curious than someone who aged normally.
I also agree with you that not going through puberty would likely make a person less aggressive.
But probably the most important effect to think about would be the social effect on a person who always looks like a child. This person is mentally an adult, and presumably would like to be treated like one, but everyone they meet reacts to them like they were a little kid. When they say something, nobody listens to them or takes them seriously. People tell them to "run along and play"; people ask where their parents are and who's taking care of them. Even their friends, people who know they're mentally an adult, have to keep fighting the reflex to treat them like a small child.
This person's approach to social interaction is built around this problem. Everything they do is focused on the need to compel people to take them seriously. They might act very aggressive, because (1) nobody will get seriously angry when threatened by a little kid, but (2) the threats just might compel them to treat the kid as a real person. They look for ways to appear more important -- standing on things to look taller, wearing formal clothing, et cetera.
They might spend a lot of time online, where their age wouldn't be visible. Or they might spend most of their time with a few close friends. They'd probably find it pretty stressful to interact with strangers -- if nothing else they'd get really tired of having the "yes I'm old enough to count as an adult" conversation over and over.
I think this effect would mostly override the effects due to hormones or lack thereof.