Extension String - Date Validation

Extension.cs

public static bool ValidDate( this string date )
{
    bool valid = false;
    DateTime targetDate;

    if (valid = DateTime.TryParse( date, out targetDate ))
        valid = (targetDate >= new DateTime( 1753, 1, 1 )) &&
                (targetDate <= new DateTime( 9999, 12, 31 ));

    return valid;

}

Program.cs

Console.WriteLine( "12/31/1752".ValidDate());                     // False
Console.WriteLine( "1/1/1753".ValidDate() );                      // True
Console.WriteLine( DateTime.Now.ToShortDateString().ValidDate()); // True
Console.WriteLine( "12/31/9999".ValidDate() );                    // True
Console.WriteLine( "1/1/10000".ValidDate() );                     // False

C# Extension for validating date within a range from an unknown string.