Okay, so I changed the title a bit from "grown up" to "getting old." I did this because I refuse to grow up. ;-)

I new I was getting older (and thus becoming a grown up, no matter how much I refuse to admit it) was the day I realized I didn't recognize any of the music on the radio. But, when I found the "classics" station, I recognized every single song. That was depressing.

As far as being an adult or a grown up, when I was able to have two cold slices of left-over pizza and a beer for breakfast without anyone there to stop me, was the day I knew I was grown up. ;-)