For me it was this past year. I had graduated from Tech school with an AAS in Networking Administration. I was hired on as a Systems Admin where I work now, got my family a nice new house. Then I began to notice how immature and infantile many of my relatives were, such as my mother in law, sister in law, and sister.
Pretty soon it hit me... "I'm a father of 2, married for 3 years, have my own house, great job, saving for 401k, don't go out anymore, quit smoking, make responsible decisions, etc., etc..... holy sh*t!!"