The human nature, we need to do something for the feeling we add value to our life. If you don't have any direction where to go, you are a sinking ship!
I believe retirement is a modern concept that you don't need to follow. You can have experiences right now instead of waiting for the ultimate age, which is simply a number.
Would be nice if after retirement, we could also return to our perfect physical condition for the last 20 years :)