i think that when you reach 100 you have learned many of lifes lessons, but still do not know all of them. If you imagine this, 100 is not really that old, while it seems old to people a quarter that age, if you think about the fact that your grandparents were/are/about to be around 60 on average so its really not that old and there are many things to be learned.

Also since the times always chage, lifes lessons change too, and the extra 100 years will create more lessons in life that will be learned.