I'll answer a question with a question. How come, did you start wondering about that? I mean, you are who you are, without needing any labels that may help the mass understand your character better - or for whatever other purpose labels like that may be used.
In short, I'm wondering whether someone else made you start wondering about that. And if yes, why is it so important that you find out.
Because in my humble opinion, if you "aren't" in fact a "man" it's not gonna change from one moment to the other. No matter how hard we try, we remain "we" in a wide sense of the word. Simply being yourself makes you seem like a kid in the eyes of some people, as a man in the eyes of some other people, and who knows in how many different interpretations around the world. So, in a way, you're not going to "transform" into a man, only make more people around you think of you as such. Which is kinda lol imo, but if it's important to you then good luck. There aren't any tricks or shortcuts. And any advice like "grow a beard" "act like Dante" or something are not really going to help you since by doing things that aren't "you" you're not becoming a man or anything else, you're only role-playing.
If someone else wanted you to be a man in their own perspective, I'd say it's their problem, and even if you try to act like one - in case you "aren't" - you'll see new problems there. That is, in case I'm correct and somebody told you so. Otherwise ignore this paragraph
It's nice to look inside ourselves and wonder, but not as productive as just living our lives to the fullest - at least, that's what I believe. ^_^