Years, ha, try life-times. If there's one thing I dislike about this manga, it's making Shigaraki the villain he is. He pales in comparison to every other villain we see, not just in power, intelligence, or simple interest, but potential. With Deku we see the potential to be a great hero, with All Might we see a great hero, with Stain we see a great villain, with All for One we see the potential for a great backstory to a great villain. I don't see anything interesting or any potential in regards to Shigaraki, the backstory was a good touch but ultimately pointless; Shigaraki is probably the worst part about this manga.
@Raffro
Two possibilities,
1) You see the Eggman resemblance.
2) He's the doctor from the beginning of the series that told Deku he has no powers.