15 Years Old

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

Answer

The person was born in 2005 B.C. (Before Christ). Therefore, he was 5 years old in 2000 B.C, 10 in 1995 B.C, and 15 in 1990 B.C.