To counter HAR's coding on fertility, I have found that by using alite's Fertility Genes mod along side VOID's Character Editor mod to work as followed.

1: During the making of your colonist as you see fit, bring up the character editor mod's window to begin the edit and click on the face icon in the bio section.

2: In the germline of your colonist, add the fertility gene of your choice to get the desired fertility (It is recommended to have the 'Show Fertility in Heath' mod for better management) and in Xeno germline, add the archite gene Ageless to completely pause the colonist's aging.

If the biological age is around 48 or higher, you can then click the biological age in the bio tab and lower it to bring back up the fertility to a better percent for the fertility genes to work their magic.

For those that really like using racial mods that requires HAR, I hope this helps. This discussion will also be repeated in alite's Always Very Fertile mod discussion as well.