Without health issue, hard for clergy to get retirement in the RCC.
Many dioceses force 'em to stay till 75! Priests are coming down the aisle in walkers, and some just sit at altar. Pathetic! 
Interesting Card. Wuerl has reached 75 but will stay on as being a cardinal in WDC is a top shelf position and what would come if retired? Seminars on EWTN? No staff and servants and evicted from his sumptuous digs
In many diocese when one leaves, dies, or has catastrophic illness & has to withdraw, the diocese's food chain is highly disrupted.  Hence, the drive to fish in foreign waters for bits.
Good news is that more sane America RC males are not digging this unnatural life.
They are finding life, a real one, on their own terms.
Now PD may find more time to focus on his writing and by withdrawing will perhaps be able to distill more spirit from his experiences. Ad multis annoys!