How to: Disable Previous Dates in Calendar Control

Here an example on how to disable  or set the calendar previous dates to not selectable.

ASPX: 
 <asp:Calendar ID="Calendar1" TodayDayStyle-Font-Underline="false" runat="server" SelectionMode="None"OnDayRender="Calendar1_DayRender" >
                <DayStyle Font-Underline="False" Wrap="False" />
</asp:Calendar>

RELEVANT CODE: 

  protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
    {
        if (e.Day.Date < DateTime.Now.Date)
        {
            e.Day.IsSelectable = false;
            e.Cell.ForeColor = System.Drawing.Color.Gray;
        }
    }