is there a way correct and scientific way of telling how old someone is?

Question

Imagine someone is born in the remotest area of the world where civilisation has not yet reached. The people do not know about the gregorian calender/s there a way that such an individual can be helped to determine on exactly when he was born.

Answer 1

Not a specifc Birthdate but they can go by the Pelvic bones, it as you get older the pelvic bone fuses together more. there was something else like the femur, can't remember.

Answer 2

bones and teeth