Calculate your age using dateTimePicker :

Just consider this window :

Now double click on OK button and write down this code :

 private void okButton_Click_1(object sender, EventArgs e)
 {
   int myAge = DateTime.Today.Year - dateTimePicker1.Value.Year;
   textBox1.Text = myAge.ToString();
  }

Now select a birthday date from dateTimePicker then click OK button.then we can see the result in text box.

OUTPUT :