Currently all baby mobs grow up after 20 irl minutes.
I think that's too quick, and baby villagers should stay as babies for at least an hour. So they grow much slower than other baby mobs.
Why: I think baby villagers add some more atmosphere to villages, to see them playing & chasing each other. It's not that common to see it, when there's usually only one baby at a time, and they grow up so fast. So I think this should be changed, especially if they'll add new AI behavior for the kid villagers too.
This would make sense too, since animals grow up faster than humans (or human-like creatures in this case).