Data type problem to save profile

 HI,

I have problem regarding to load default page which contain profile field data, when I run the page, the following error occure:

 CS0029: Cannot implicitly convert type 'System.Web.UI.WebControls.TextBox' to 'System.DateTime'

The page contain field table and submit button, part of the code as below:

default.aspx

 protected void Button1_Click(object sender, EventArgs e)
    {
        Profile.FirstName = txtFirstName.Text;
        Profile.LastName = txtLastName.Text;
        Profile.DateOfBirth = txtDateofbirth;
    }

web.config

 <profile>
        <properties>
          <add name="FirstName" type="Sys ...