When is one middle-aged?

You know you're middle aged when you get an AARP application in the mail. Seriously, for me the moment came when I took my husband to a Heart concert and I'm rocking to the music, looking around and I realize that everyone there was 30 years older than we thought we were. It made me stop and reflect on where I had wanted to be and where I was. I have to say I really like being 50 something. I have a maturity I didn't have, a confidence I've certainly earned. And all the young people think I'm eccentric (or crazy). Works for me.

I think the term "middle-aged" is probably based on the current average life span. For example, the average life expectancy in the US is 77.9 years, so one would reach middle age at 39. However, this theory leads one to wonder when middle age ends, and senior years begin. We seem to have clear cut notions of the line between infancy, childhood, and adolescence, but I suppose the glut of baby boomers who are still very active into their later years has blurred the line between middle age and old age. Or maybe this is all just bluster, and middle age is defined by each individual :)