Conversion failed when converting datetime from character string

how to solve this error?

Page Design

<td>
                         <asp:TextBox ID="txtDateOfBirth" runat="server" ></asp:TextBox>
                         
                         <cc1:CalendarExtender ID="txtDateOfBirth_CalendarExtender" runat="server" 
                             Enabled="True" TargetControlID="txtDateOfBirth">
                         </cc1:CalendarExtender>
                         
                     </td>

Code Behind

protected void btnsave_Click(object sender, EventArgs e)
    {
     Admin aad = new Admin();
aad.addProfile(txtDateOfBirth.Text, Convert.ToInt32(txtAge.Text.Trim());

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