how to display year of given date of birth in lable

Label1.Text = Convert.ToDateTime(TextBox1.Text).Year.ToString();

<div>
       <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
       <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
       <asp:Button ID="Button1"
           runat="server" Text="Button" onclick="Button1_Click" />
   </div>