#pas
{Взято с сайта http://www.swissdelphicenter.ch/en/tipsindex.php }
//==================================================================
function CalculateAge(Birthday, CurrentDate: TDate): Integer;
var
 Month, Day, Year, CurrentYear, CurrentMonth, CurrentDay: Word;
begin
DecodeDate(Birthday, Year, Month, Day);
DecodeDate(CurrentDate, CurrentYear, CurrentMonth, CurrentDay);
if (Year = CurrentYear) and (Month = CurrentMonth) and (Day = CurrentDay) then
begin
   Result := 0;
end
else
begin
  Result := CurrentYear - Year;
   if (Month > CurrentMonth) then
     Dec(Result)
   else
   begin
     if Month = CurrentMonth then
       if (Day > CurrentDay) then
         Dec(Result);
   end;
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
Label1.Caption := Format('Your age is %d', [CalculateAge(StrToDate('01.01.1903'), Date)]);
end;