One of the three skills of most of my Esteemed Elders is Doctor. In the first few games I played, I often chose Building as one of the skills, but since that is so time consuming, I changed to Medicine. As soon as a child turns 14, I cross-train it by dropping it on the crops, the ocean, and equally on herbs and at the research area. I dont set a preference skill. Every time I open the game, I check the skill bars, and when I notice that some of my villagers are getting behind in medical skills, I train them on the herbs (in the right upper corner you can train three villagers at the same time). In that way, they get their totem ten years earlier than the villagers with building skills (I do need some builders, of course).