What's the difference between 45 and 45?

45 years old means nominal age, 45 years old is a birthday, not a real age.

45 years old is the date of birth in the solar calendar, and 45 years old is calculated according to the actual age of the lunar calendar from birth to the present. The lunar calendar, that is, the current traditional calendar in China, belongs to the yin-yang calendar, that is, the lunar calendar and the solar calendar. According to the change cycle of the moon phases, each moon phase changes to one month, taking the tropical year of the sun as the length of a year, and adding 24 solar terms and setting leap months to make the average calendar year adapt to the tropical year.