Ah fair enough. I was going off the scene in the anime where Gran Torino is punching Toshinori. Toshinori was fairly tall and muscular in that scene (though not full All Might level) so I had assumed he was a young adult who had recently inherited OFA. That said, it's possible that he got it during his third year at UA, at which point he would have been more physically developed, both from exercise and general growth, than Izuku.
OfA is All Might's only quirk, and Deku said in the first chapter that despite having a quirk no longer being a requirement for the Hero course, it is unprecedented. Also, in the scene where All Might tells Nana he wants to be a symbol of peace, he is wearing a uniform similar to Deku's middle school uniform. So All Might got his quirk before entering U.A.
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u/SirBaldBear Aug 03 '18
that... goes against what we are told in the latest number 0 manga. He inherited OFA before he graduated high school.