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Like for instance, if a villager suddenly learned to be an expert marksman (just throwing something off out as an example) would I be able to have him perform umm....like say an assassination right away? Or would other tech have to be purchased first? OK my examples are really awful, but hey.


Two things on this:
  1. No, not until you're 14.
  2. Yes, you do need to purchase technology first.

The 14 year old thing is a technicality. The bonus you gain when said child acquires their skill represents the work they would perform over the course of their childhood.

Just because you have an expert farmer, he doesn't magically gain a fishing rod. By this same token, your marksman will need to rely on throwing rocks until someone invents the bow and arrow.