Because we allow privacy during conception, but the birth is rather public. For example when a new member is added to a royal family, the entire court gathers to witness the event.
I was talking to someone on the bus from one of the asian countries. he said in his particular country, they do count the 9 months spent inside the womb. he said "when i left my home country, i was 39 but when i moved to Canada, they counted me as 38"
This post was edited by Skunky Stinkerson at February 21, 2017 9:30 PM MST
This is an interesting point as in the western world you are noted as been zero on birth however in many Asian countries (I'm half Korean ) on birth your age of reckoning is one at birth. so if you ask most Asian people born in Asia (not so much those born in the west) you will find they say there a year older than the west will say. Plus the age is increased on the first of the new year each year for a lot of official things not on birthdate.
This post was edited by Suewiang at August 13, 2017 12:55 AM MDT