One.
I only played young adults early in the Sims 4 because I did not like how sims aged up from babies to children and then from children to young adults. I have never considered TS4 teens to be teens. They look too much like young adults.
Now that we have toddlers, Parenthood, ( plus a teen height mod) I am playing families.
I did age all my CAS born young adults down to toddlers and gave them parents in CAS.
The first batch have graduated Uni and are in starter homes. I an now rotating to the others.
By the time I get to generations 3-5, the Sims 5 should be out.
