Time in short supply

Why is it that the older you get, the faster time passes?  When you’re a kid, you have all the time in the world.  As you grow older, time passes exponentially faster, until before you know it your life is over.  OK, that sounds a bit fatalistic, but it does seem that time passes more quickly as you age, doesn’t it?  I suppose that it slows down again after you retire and your children leave home.  I don’t really know, because I’m still a long way from retirement.  I just know that time seems to be passes more and more quickly for me with each passing day.  Today is a perfect example.  In the morning I woke up and had breakfast with my son.  Then we went outside and played for awhile, and my wife went shopping.  We went back inside and played some more.  At lunchtime we had lunch.  When he took a nap, I did too (naps must also be a sign of aging!).  At 5 o’clock I met someone for a two-hour discussion on a serious situation with the community association, then at about 7 o’clock I joined my wife and son at E-Mart for shopping and dinner.  We returned about 9 o’clock and put our son down for bed.  I went online and did some e-mailing, and now I’m here writing this blog.  It’s 11:45 in the evening, and another day will soon be over.  Although a lot happened today, I felt that there was so much I did not do because I did not have the time.  For my son though, it was nice long day full of fun and play, just like the yesterday and the day before.
Do you think time passes more quickly as you grow older?  If so, why?