It's a pretty goddamned short list.
Benitez at 17
Pipino Cuevas at 18
Manny at 18
Tony Canzoneri at 19 (though he got a draw at 18 for the bantam crown IIRC)
Lionel Rose at 19
Ben Villaflor at 19
Those guys all won lineal/undisputed crowns
Hiroki Ioka at 18 won the first 105 title if you want to count him.
I think that's it. 135 years of boxing as we now know it and it's been done only 6-7 times.
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