This is inspired by the lyrics "in 1969 I was 21." This can be helpful for people who were known to be in college, the military, etc at a given time.
Parameters:
(1) age
(2) given year for age
(3) target year for age
approximate year of birth =
= (given year for age) - (age in years)
age at target year =
= (target year) - (approximate year of birth)
One obvious modification is to include more specific information about the birthday.
