23 is not a good limit, there are very few fighters ranking in top 50 and aged below 23, less than 30-40, so most of them would be in the list. 25- p4p would be a better list.
Naoya Inoue at 21 is a complete beast of a boxer. Jose Benavidez is only 22 years old. Saul Alvarez and Juan Francisco Estrada are both 24 years old as of today, so they just miss it. A lot of great fighters are 25 and 26 right now too. Few established at 23 or under though.
That's hard. Inoue is the #1 by miles. I can only think of Micki Nielsen/Erik Skoglund or Felix Verdojo, who have a bright future. Maybe even Vincent Feigenbutz. But boxing is no young men's game (like soccer).
