Personally what I meant about growing up is, that yes there is SOME growing up to do! Whether you like it or not. When you have other responsibilities you didn't have when we were younger, but now have to make the CHOICE to keep the house clean, pay the bills, spend time with the kids and family, etc etc. Then you have "grown up" so to speak. Can't play games all day. Because you know what are the more realistic priorities that take up your time now.
And then on top of that, yes, getting other interests too. That's the other part of it. Then again, if you have developed other interests or lifestyle changes, it's probably because you are older too! Like I do have alot of free time still, yet these days I now take care of myself better and workout now, I go biking, or I'd rather just relax and watch tv or a movie, rather than gaming.
Not saying I don't game or get excited to play certain games, it's just nowhere near the level as it used to be.