Some people may mistakenly think that age is exclusive to the elderly, but in fact, age refers not only to the elderly, but to all ages in life. This concept is also reflected in ancient culture and philosophy. For example, the "destiny" in the Book of Changes means that the whole life cycle of human beings should conform to the laws of nature and the essence of life.
In a word, calendar year is an abstract concept, which refers more to all ages in human life than to a specific age.