This is the 26th most frequent Spanish word.
año
"Year"
Here, 'año' is used to refer to the age of the son, meaning one full year of life.
Tiene un hijo de un año de edad.
He has a one-year-old son.
In this sentence, 'año' refers to the current calendar year.
Este año he viajado a España por primera vez.
This year I traveled to Spain for the first time.
In this example, 'años' is plural and indicates a span of time in years, referring to a point in the past relative to the current time.