The TODAY Function is one of the most popular date funtions and it returns the serial number of the current date.
Today function may return to a date depending on your cell format, and you can check the serial number by changing the date format.
Today function can combine with Year function to calculate a person's age. For example, if you know a person who was born in 1977, and you can you using the following formula to get the person today's age.
=YEAR(TODAY())-1977, the person is 39 years old.