I'd say I discovered and have started reading Jump since 2006 and because Naruto, then discovering One Piece, Bleach, Death Note, HxH, D.Grayman, Gintama, and Reborn were also in the magazine.
I inmersed fully in Jump in 2009 though, when Bakuman To Love Ru, Toriko and Nurarihyon first, then Kuroko, Beelzebub and Medaka started serialization. At the same time I was learning about more titles like JoJo, Eyeshield21, or Hikaru no Go. 2012 was the final consolidation thanks to Nisekoi, AssClass, Shokugeki and Haikyuu. And in 2014 My Hero Academia was the first hit manga I started reading since the very first chapter in Jump.
My first Jump experience is "Mazinger Z", then Dragon Ball, Saint Seiya and Captain Tsubasa, then Kenshin and One Piece (and City Hunter in lesser degree), then Yu-gi-oh and HxH, then Kochikame, Bobobo and Shaman King, then the Internet era with Naruto, Death Note, Bleach (and later Prince of Tennis, Reborn, Gintama and D.Grayman) while discovering at the same time Fist of North Star, Slam Dunk and Yu Yu Hakusho (I had a previous first contact with Yu Yu Hakusho, Kinnikuman, and Dr. Slump though, but I didn't know catalan language)
PD: I'd say Saint Seiya has been the very first manga I've read. I remember reading Yu-gi-oh in 2002, when I knew One Piece from TV and I didn't know anything about the existence of Shonen Jump or Naruto.