I discover that at 23:59:60 UTC 30 June 30, 2015, I will age by more than expected.
The time it takes the Earth to rotate (a day) is getting longer by about 0.002 seconds a day, as it is ever so gradually slowed down by the drag of the tides and the atmosphere. It’s not precise enough to define a second as simply as an 86,400th of a day. It’s now 9,192,631,770 oscillations of a 133Cs atom at rest and at 0°K, as measured by ultra-accurate atomic clocks.
Since 1972, 26 or so leap seconds have been inserted in our timekeeping to keep Universal Time in step with the atomic clocks, on the advice of the International Earth Rotation and Reference Systems Service, thus increasing my age by a total of about 1.2235*10-6%. Scandalous!