Three turning points in life...

I read this from somewhere but I can't remember which book. It goes something like this:-

A person faces 3 turning points in life that one should bear in mind:

• The first is around the age of 17 or 18 when one may become tainted through the bad influence of friends
• The second is around 30 when one may become arrogant about things, failing to show respect even to venerable seniors
• The third is around 40, where one may grow bored with life and be given to reminiscing about the past, thus growing weak at heart

I think I had reached the third turning point a little too early...