He is a freshman and yes has played all year but he has not played on defense in every game this year.
Quote from the article by Ben Garrett:
Enter Eli Jordan Sexton. In his first season of high school football, Sexton hasn't played on the defensive side of the ball in every game. But he got a big opportunity on a big stage in the Indians' first round playoff win in Elizabethton on Friday, and he came through in a big way. In fact, it's not unfair to say that Sexton was a big reason why the Indians won the game — or, at least, a big reason why they shut out Happy Valley. The freshman forced two fumbles and recovered one, including a big stop on the Warriors' most promising drive of the night, after they had reached Oneida's 21-yard-line.
Link to the article:
https://www.indherald.com/2023/11/05/youth-fuels-oneidas-surprisingly-good-defense/