What is the proper age to tell your child that he came from your heart & not from your tummy...and how do you tell her? Thanks peeps!

I dont really care about the age. As soon as my son starts talking or begin to have some understanding, I already thought him things like penis (not kukubird), vagina, where he came from and 2 ways how babies are born. He knows that he came from my tummy as he is a c sect baby.