The constant crave.
In youth you crave for more age and responsibility. But are not given it.
As an adult you crave for more time, and have responsibility handed to you, whether you wish for it or not.
As an old man you will have more time than you need, yet crave for youth. Have responsibility taken away from you, whether you wish to keep it or not.
So you will get more time than you need, yet still crave youth. Have more responsibility than you can handle and then have it taken away.
But, what about craving and wishing? That will remain the constant, unless you wish it away. The irony.