Reporting
We aren't aware of studies on

We aren't aware of studies on this. It could be that the saying may have come about because if one only counts a person's age as the number of official birthday dates that s/he passes over the years, then a person born on leap day will not have as many birthdays as others, and therefore will be "younger" and have a longer time to reach old age. For example, someone 100 years old in normal reckoning, might be only have lived through 24 or so leap days, so might also be considered as being in his/her 20s.