The social media posts, which no longer appear on Allen's page, contained racial slurs and offensive language, according to Yahoo! Sports.
Allen acknowledged the tweets, most of which were from 2012 and 2013, to ESPN's Chris Mortenson, saying, "If I could go back in time, I would never have done this in a heartbeat. At the time, I obviously didn't know how harmful it was and now has become.
"I hope you know and others know I'm not the type of person I was at 14 and 15 that I tweeted so recklessly. ... I don't want that to be the impression of who I am, because that is not me. I apologize for what I did."
University of Wyoming head football coach Craig Bohl released a statement in regards to his former quarterback.
"I know Josh has apologized for the Twitter comments he made while in high school," said Bohl. "As a member of our football team, he had great relationships with his teammates and our fanbase. During his time at Wyoming, he embraced diversity. We wish him all the best on his big night."
Allen has been rumored to go as high as No. 1 overall to the Cleveland Browns, and most analysts have the quarterback being selected in the top 10.
Could the resurfacing of his controversial tweets affect his draft status? We've seen in the recent past that late-stage reveals can have a tumbling effect on a player's stock -- like Laremy Tunsil's gas-mask bong video in 2016.
Allen's tweets will also lead to post-draft questions about how the quarterback might be accepted within the locker room and whether there are any character concerns. All these issues will be something Allen and the team that drafts him Thursday night must be prepared to answer.