Sometimes Spanish birth or baptism certificates offer information about the parents’ age. That is very useful information to continue the research. But we do not know the exact birth date so there are two possible years to research. If the records are not indexed, that may take a lot of time, but it is possible to restrict the search with a simple calculation. It is easier to explain it with an example.
We have a birth certificate for a baby born on April 1st 1834 and it says that his father is 31 years old. The simple math with the years would indicate the father was born in 1803, but that would not take into account the months. The accurate way to find the father’s birth certificate will start researching on April 2nd 1802 and finish on March 31 1803.
If born on April 1st 1802 he would be 32 years old, and if born after March 31 1803 he would still be 30.
This is the most effective way to find a record based on dates as we reduce the months we are researching.