I want to make a manchild character but I don't want him to be obnoxious, so I want to know what will makes people actually like manchild characters
I don't know any likeable manchild characters. The term itself implies a negative image. You can have likable childlike adults, but that's different.
Are you talking about a guy with adolescent pastimes? Or is he dangerously irresponsible. I picture a frat hero of the last generation still crashing parties. I'm curious how severe his sins are. You have to put yourself in his shoes. Even with the darkest villain, if you give him a chance to prove himself in even a small way, that is pretty redeeming to the reader. So don't make it a complete caricature. Maybe the people around him see one thing, his edgy, carefree behavior, but then the reader sees something deeper, some dark concern or heavy responsibility that no one knows about. Perhaps he's venting with a flippant or trivializing behavior, or even trying to distract others. Maybe he's distracting himself. Maybe he's running from a problem that's about to catch up with him. Give your characters the benefit of the doubt. Heck, that's going to shape the whole character and the plot.
Those around him may be sheltering him against his will. This could be well-intended or more sinister and self-interested. The latter wouldn’t even need to be conscious. A mother or father who can’t stand the idea of their widdle baby growing up and thus undermines his efforts to mature and become more independent, maybe. The Waterboy is actually a really good example of this one. Bobby Boucher is pretty much a textbook manchild, but his manner, the bullying he faces, and the fact his childishness is the result of isolation imposed by his zealot mother—who fears he’ll leave her like his father did—all endear him to the audience.
This is really good advice. I often write characters that are unlikable to the outside world but more likable to the readers because they can see other aspects the world can't. That's also why I use first person so often. It's a nice way to get even closer to the character. Though you don't have to use that POV if you don't want to. It's just something that I do.
Don't worry. His adoptive big brother just want to protect him, but since he end up sheltering him from harm, he grow up into a really naive adult who doesn't know the outside world, especially since his adoptive brother is an alien who take him from earth from early age and he doesn't really know his fellow human. His biological parents kinda abandoned him
I can't recall reading one I ever cared for. However, Andy from Parks and Recreation was a likeable man child. He was an unemployed starving artist type, who had big dreams but was lazy...initially. The type of guy kids love, because he's one of them at heart. Caring, but in a goofy manner, would write a silly song to win a girl over, but they usually backfire. I'd say a good start would be something along those lines. The favorite uncle that the parents all roll their eyes at. Sort of simple minded but only because they lack real world experience that you can give them along the way.
Every Will Farrell character, basically, haha. Not a big deal, but I wouldn't associate the term man-child with this. That definitely conjures immature, obnoxious, but probably fun-loving men doing inappropriate things in a pratfall kind of setting.
I think of "failure to launch" tropes. A guy who's twenty-two, wakes up at noon and plays XBox. (Living the dream.)
