Actually, when people start to reach the age of 30 they start to behave like adults. Forget stupid artificial legal age limits like 18 or 21. There is a strange trend that people try to prolong their younger days more and more beyond 18/21, and refuse to grow up. When it comes to taking responsibility for their actions, their work, etc., when it comes to stopping to behave stupid and being proud of behaving stupid then around 30 is indeed the mark to look for.