Where did you get that after 13 you don't need to write numbers? That is possible with any number, if they put it in the database. Not all sentences have the option. Some do, some don't, but it's not related to the number itself.
Well, in English I only know the recommendation given by handbooks of style to spell out "whole numbers from one through one hundred, round numbers, and any number beginning a sentence". In German the DUDEN recommendes this up to twelve.