The distribution of the birthdays of the cardinals, by and large, is arbitrary — though there have (and will be) a few instances where a prelate was created, when he was, because his birthdate ‘fitted in’ relative to the ’80-year’ cutoff. We just had two cardinals, Abril y Castelló & De Paolis, turn 80 within the space of two days. But prior to that the last cardinal to age out was 5 months earlier.
And we are going to see that again. The next cardinal to age out will be US Cardinal Roger Michael Mahony, on February 27, 2016. So that is the next scheduled change to the College — barring deaths.