Just had a Elasmotherium couple make a child that is older than the mother (Mother is 9 and the child is 10) there was no sign of pregnancy that I saw with the female, She was grown witch chicken essence and the child emerged from the father. This is their first born both were max happiness.

Also worth mentioning the parents were the only elasmotherium that had been in the world prior and none had been created before them. I was present for the birth, This is the newest version of the mod