you know who was self taught? cavemen...they didn't do things too well for a looooong time.
even Batman had a half dozen of the best teachers...
and chances are we won't start out as a billionaire genius with an obsession for justice.
How do you know your mage didn't study for years alone studying books for reference? It's a bit different to a cro-magnon smashing rocks together in an attempt to create a spark, and even then it's doubtful that it wasn't a part of learned culture as shown in existing chimpanzees. A lot of people teach themselves things, like learning a new language or playing an instrument. It's just about using the resources you have available at the time, as opposed to hiding in a cave and trying to figure the whole thing out yourself.
hey man, I'm not arguing FOR my specific approach per se...I'm simply arguing against having a class that has specialized skills with no reason whatsoever.
I want there to be a damn good reason why i'm such a good lockpick, healer or swordsman...
Then come up with your own roleplay background for the character, it's what people have been doing for years.