date to int

Question

here i write a code to convert user given dob is stored as a age in db

but it shows a error --------------Failed to convert parameter value from a String to a Int32.

 i use stored procedure for it

in .CS button _click

cmd.Parameters.Add("@age", SqlDbType.Int).Value = at.Text;

in stored procedure

@age int-----------------datatype

in table

age  int

public int Age(DateTime dt)

    {

        DateTime today = DateTime.Today;

        int age = today.Year - dt.Year;

        if (dt > today.AddYears(-age))

            age--;

        return age;

    }

    protected void at_TextChanged(object sender, EventArgs e)

    {

        int age = Age(Convert.ToDateTime(at.Text));

        Response.Write("Age:" + age);

        Label8.Text = "Age" + age;

    }