Well, not going back far—Dragonlance, Forgotten Realms, Dark Sun are all book worlds that were created in gaming sessions and then written out. The characters grow along as they leveled in game.

Mercedes Lackeys series regarding Valdemar often centered around a protagonist who know little and has to be trained by the Heralds to get a destined job done. Sometimes the case is they know how to do SOMETHING—but not be a goody goody on a white horse.

Specific trilogy that I loved from that set is the Last Herald-Mage of Valdemar. Guy starts off as a fop is a noble. Ends being the last line of hope for his kingdom. Really demonstrates how growth and personal sacrifice can be connected.

Dragon Riders of Pern by Anne McCaffery all center around taming & riding dragons to protect the world from an all consuming thing which falls from the sky. MC is usually a new recruit in book 1

Michael Stackpoles Dark Glory War book features some friends on their first official day as adults ending up fighting for their lives. Over the next 4 books they train until they are fighting the individual their entire culture is meant to survive.

Note I’m am being a touch vague to avoid spoiling any that might be new to YOU.