Yes, you do need to "grow up", simply because you may be 21 and old enough to vote, marry, die for your country, go into pubs/clubs etc etc, but you are still at a very young, vulnerable and impressionable age.
I've been at that age, obviously, a long time ago, and believe me, not only do I know what I'm talking about, but I do so from many years of experience of being in law enforcement and can assure you that your experience is one predominantly peculiar to younger members of society as opposed to older people.
How many pensioners do you normally see involved in what basically amounts to gang fights? You don't. Overwhelmingly, those taking part are of your age group and the main reason for it is immaturity. Give it another 20/30 years and you'll realise that what I'm advising you is true and accurate.