On records >from Poland >from the 1800's, are the reported ages
a) age at last birthday. This means that person who was 1 day
less than 20 years old would be reported as 19, and that a
person's numerical age advances on his or her birthday. The U.S.
census uses this method. This method is also used for stating
age minimums, such as you must be 13 to count as part of a
minyan, 18 to vote, etc.
b) age rounded to the nearest year. This means that a person
who is 19 years and 7 months old would be reported as 20, and
that a person's numerical age advances half-way between
c) "year of life" or age at next birthday. This means that a
newborn up to 364 days old is 1 (in the first year of life), then
the age is "2" (second year) >from the first anniversary of the birth
to the second, etc. A person's numerical age advances on his or
her birthday. This method is used for the practice of saying the
Tihillim (psalm) corresponding to a person's age (the youngest
possible age is the 1st year of life [birth to the 1st birthday], and
the oldest is the 120th year [>from the 119th birthday to the
120th birthday], because Jews have not lived beyond their 120th
birthdays since Biblical times.)
I am trying to calculate which dates to search for birth records of
individuals whose ages are given in their marriage or death
records or in their children's birth records.