It can go upto 23 years on account of the student house being very far from the school house. How long are people students in banished? If there is a herbalist staffed there then the villager will have their health increased. They will attempt to get a herb from the stockpile, and if one is present they will take it to a herbalists hut. When a villager has low health they will attempt to visit the herbalist. There are no diminishing returns on workers that is to say that the thirtieth worker will produce just as much iron or coal as the first worker (all else being equal). Mines need to be placed on the side of a hill or mountain and have a maximum capacity of 30 workers.