What makes a person a “real” grown-up?

Re: “Facebook Members are Aging Rapidly” Published in the Bee on Feb. 26, 2009. The writer says “(Facebook) is exploding in popularity among grown-ups. The real kind. The kind over 35.” Is that what defines a grown-up? Being over 35? What makes a forty year old man who plays video games and drinks all day any more responsible than a twenty-five year old with a wife and kids, working two jobs to get by? I don’t think that our society can afford to be so stereotypical that we classify adults as only someone over the age of 35. I know plenty of younger people who are more responsible than these so called grown-ups. I’m not saying these things to “bash” adults, but merely to point out that the number of years you have been on this earth does not, in any way, determine your maturity. What’s your opinion? What makes a person a “grown-up”?