I've had quite a few villagers from different villages become master doctors without any encouragement from me. I've even saw trainee and adept doctors examining the herbs. I've got to say this really surprised me since most of the docs prefer relaxing on the beach.

In the beginning of a game, I want the puzzle, so, of course, I take an adult villager by hand to all the herbs. Then, when a person or persons becomes sick, I rush children around to heal them. This way my kiddies will be apprentice doctors.

In one of my earlier games, I used the same child for healing; she became a master doctor at 15.