Grandpa said to his grandson on his birthday, "I just had 18 birthdays." Do you know why? How old should grandpa be this year?

Grandpa should be 72 years old this year. .

Reason:

Grandpa's birthday is in the lunar calendar of a certain year. There are two February in a year, and the second February is a leap February. The frequency of leap February is second only to leap March, and the frequency is moderate around AD 2 1 century, generally once every 19 years (such as 2004 and 2023). Since then, the frequency of leap February has gradually decreased to become a rare leap month, which occurs once every century from the 25th to the 28th century, and there is no leap February in the 29th, 30th, 36th to 38th, 40th to 44th centuries. The 29th.

There is a leap in February every four years, that is, February 29th.

Grandpa has 18 birthday, so multiply 18 by 4, and grandpa is 72 years old.

Extended data:

What is leap February:

There are two February in the lunar calendar year, and the second February is a leap February. The frequency of leap February is second only to leap March, and the frequency is moderate around AD 2 1 century, generally once every 19 years (such as 2004 and 2023). Since then, the frequency of leap February has gradually decreased to become a rare leap month, which occurs once every century from the 25th to the 28th century, and there is no leap February in the 29th, 30th, 36th to 38th, 40th to 44th centuries.