It might sound silly, but I actually am looking forward to retirement. It is still a good twenty years away for me, the standard retirement age for men currently being 65 in Australia - although it might be later by the time I get around to it. Few people regard retirement as the end of their active life - most retirees would see it as finally the opportunity they have always been waiting for: the chance to do the work they really want to do, rather than the work they have to do.
Priests - and bishops for that matter (see the side bar in Cooees) have their retirement age set at 75. Cardinals cannot vote in a conclave beyond 80. The pope is the only one whose office lasts until he dies. All this seems fair to me. The longer working life of priests has nothing to do with the priest shortage. There is simply something about celibacy seems to preserve the priestly caste, so that their working life extends longer than with us mere mortals. But even they need a rest finally, and it would be unjust of the Church to demand they continue full pastoral responsibilities beyond that. Of course, the character of priesthood lasts to the grave (and beyond!), and so a priest can and should still certainly spend his retirement doing priestly things.
Which reminds me of a good joke (best told with the right voice, but you will have to make do with the print version):
It's Sunday, and Father gets up into the pulpit: "My dear people. The Holy Father has just raised the retirement age of priests to 105. And so, you see, I shall be with you another three years..."