Speaking from a cellular perspective, that is!
The first cell distinct from the parent to offspring, appears while a fetus is in the womb. Since Nancy Reagan's mother was born on July 16, 1888 there is no doubt the egg that the former first lady came out of formed in the year 1888. Nancy Reagan's mother, Edith Luckett Davish, was born under present Grover Cleveland. Thus Nancy Reagan's first cell appeared on our planet sometime in the early spring of 1888.
What this means is, that Nancy Reagan on one biological level will turn 126 years old in the year 2014!!