How is the birth year calculated?

The calculation of the natal year is as follows

According to the age (birth year): 12 years old, 24 years old, 36 years old, 48 years old, 60 years old, 72 years old. Every 12 years added is your own natal year.

According to the imaginary year (birth year): 13 years old, 25 years old, 37 years old, 49 years old, 61 years old, and 73 years old are the same plus 12 years old, but the base number is different.