Read this somewhere and I thought it's very insightful:
It seems that when we are children, the time sprawls before us. Some might call this time of your life, slow or long time. I can remember Summer days, when I was about 8 years old, that seemed to go on forever. You were always in a hurry to make time go faster because you thought that if you could hurry up and grow up then life would be a lot more fun...
Then you become an adult and your life starts to move a bit faster. Some might call this normal time. You just seem to have just enough time in the day to get things done and the days pass by tick-tock... You wish for more time in a day but chances are if you had more, you would find more ways to fill it so you ultimately would never have enough, time that is.
Finally you become old and time really speeds up. Days pass by in a blur and your don't know where all the time has gone. You long for days past and feel everything just slipping away. You go slower but everything around you seems to be going by at a hyper-speed. By the time you wake up in the morning and start your day, it's already almost time for the day to end.
I guess the lesson I get out of this is that it is so critical to live for the moment because when you are young, that moment is beautiful, when you are middle aged, that moment is important, and when your old, that moment is a blessing.