function DateExists(Date: string; Separator: char): Boolean;
var
 OldDateSeparator: Char;
begin
 Result := True;
 OldDateSeparator := DateSeparator;
 DateSeparator := Separator;
 try
  try
  StrToDate(Date);
  except
  Result := False;
  end;
 finally
  DateSeparator := OldDateSeparator;
 end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
 if DateExists('35.3.2001', '.') then
 begin
  {your code}
 end;
end;

function ValidDate(const S: String): Boolean;

BEGIN

 Result := True;

 try

  StrToDate(S);

 except

  ON EConvertError DO

  Result := False;

 end;

END