A boy becomes a man the day he decides. Becoming a man is not necessarily a product of biology, it is a product of a decision.
It is a decision that interestingly can be put off for as long as you want.
You cannot start any serious work or project without making this decision to take responsibility. Becoming a man means you are ready to step into your own space in your own right. It means you are ready to believe in yourself and start taking exercising some independence.
Sooner or later, everyone needs to man up, some of us manned up sooner than later and accepted responsibilities, some others evaded for as long as they could, until they were finally kicked out and forced to get to work.
You need to become a man, you need to accept responsibilities, the sooner you realise it is inevitable, the better.
Be bold, make that decision today.