It is commonly thought, and asserted in the Meejah, that a Bishop is obliged to submit his resignation when he has completed his seventy fifth year of age.

This is not quite accurate.

What Canon 401 (1) requires is that the Bishop rogatur [is asked] ut renuntiationem ab officio exhibeat Summo Pontifici. This is based upon Christus Dominus [21] of Vatican II, which is vaguer; without mentioning