Delivery times during holiday season tend to take longer than other times.
Delivery before Christmas is NOT GUARANTEED for shipping option other than EMS.
Every year, many packages sent by standard airmail even after December 1st do actually arrive before Christmas, however some don't. It is really depend on how busy your country's post office and customs gets or it is often just luck. EMS would be the best option to select if you would like to make sure to receive your package before Christmas!