// Save today's date.
var today = DateTime.Today;
// Calculate the age.
var age = today.Year - birthdate.Year;
// Go back to the year the person was born in case of a leap year
if (birthdate.Date > today.AddYears(-age)) age--;
但是,这假设您正在寻找 西方 的年龄观念,而不是使用东亚估算 。