How Age is counted in the United States
In the United States, a person's age is counted starting from physical birth (rather than, as in
some cultures for example, from conception).
Newborns start at zero, and each passing of a 12 months period from the original date of
birth adds one year to the person's age. So, for example, if a child was born on February 9th,
2000, the same child would be: 1 year old on February 9th, 2001; two years old on February
9th, 2002; and so forth.