Restrict Selecting Date from Calendar Control

Question

I have 2 textboxes, the first textbox is a date from the database and the second textbox is asp:calendar. Now, this is what I want to achieve: Textbox2 cannot select a date older that what is in textbox1. Below is my code but it is not working.

 

html and c# code:

 

 <ajaxToolkit:CalendarExtender ID="calFirst" runat="server"
                TargetControlID="TextBox1"
                CssClass="MyCalendar"
                Format="MMMM d, yyyy" />

<asp:TextBox ID="TextBox1" runat="server">asp:TextBox>

<br>
<asp:TextBox ID="TextBox4" runat="server">asp:TextBox>

            <asp:ImageButton ID="ImageButton1" runat="server" Height="17px"
                ImageUrl="~/img/calendar.png" OnClick="ImageButton1_Click" Width="21px" />
            <asp:Calendar ID="Calendar1" runat="server"
                OnSelectionChanged="Calendar1_SelectionChanged"
OnDayRender="Calendar1_DayRender" Visible="False">asp:Calendar>
protected void Calendar1_SelectionChanged(object sender, EventArgs e)
        {
            TextBox4.Text = Calendar1.SelectedDate.ToShortDateString();
            Calendar1.Visible = false;
        }

        protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
        {
            DateTime date = Convert.ToDateTime(TextBox1.Text);
            if (e.Day.Date > date)
            {
                e.Cell.Enabled = false;
                e.Day.IsSelectable = false;
            }
        }

        protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
        {
            Calendar1.Visible = true;
        }