A man's age doesn't make him grown his priorities do. A man can still think and act like a child regardless of how old his biological age may be, and age alone does not determine being grown up. There are many men in their 30s, 40s, and even older who do not take care of their responsibilities, creating babies but failing to be part of their children's lives once they are born.
When you have your priorities in order then you are grown, even if this occurs in your late teens or early twenties. Taking personal responsibility for their actions and the consequences is what defines a grown man. Age is irrelevant, and only shows how long someone has lived and not what they have learned during their life so far. A real man who is grown and mature will understand that their family and other responsibilities are top priorities, fund and hanging with friends takes a back seat when a man is truly grown.