...you have to do subtraction in your head to determine your age. Remember back when you younger and you just always knew your age? "I'm 13!". Now it's along the lines of "Well, oh, 2009 from 1965...I'm 45".
...instead of haircuts, you start to think about how you can style your hair so that the receding parts aren't as noticeable?
...you genuinely don't give a rat's a$$, for the most part, about what others think?
...you don't even bother to listen to most Top 40 radio stations?
...the high school you attended doesn't exist any more?
Yes, growing old is certainly grand, grand indeed.