The chances of them constantly saying 'no' depend on the villager entirely! Liking or disliking learning can effect how likely they are to say "N0" when you're trying to teach them the skill early on. Liking or disliking work will effect how often they like to wander off-task. If he likes building, or science, or etc, that will be a good job for him. If he dislikes wood or lifting, building is a bad job, and so on.

It all depends on the villager. However, you can train him in healing by having him heal the sick even before age 14. I would save research or parenting for later in life, since building and farming involve a LOT of walking-distance, and walking long distances makes it very hard for the elderly to gain skills. They're just so slow!