I want to add age in fractions like 0.5, 1.5 etc.,

Question

I want to add age in fractions like 0.5, 1.5 etc., in my aplication, 
the data type was int earlier, i changed it to decimal but when i put decimal points the aplication exits.
there are some conditions too.. part of the code i found is given below

 private void txtAge_TextChanged(object sender, EventArgs e)

        {

            if (txtAge.Text != "")

            {

                if (Convert.ToInt32(txtAge.Text) > 18)

                {

                    txtFees.Text = Convert.ToString(2);

                }

                else

                    txtFees.Text = Convert.ToString(0);


plz help