Publication date does not determine whether a source is "academic". While newspapers are generally not considered academic, prominent newspapers like The New York Times and The Wall Street Journal are both highly regarded, reputable newspaper sources. But they are still considered to be "popular" sources. If your professor only wants you to use "academic sources" in your paper, they are likely excluding newspaper article, regardless of the article's publication date. This chart highlights some of the differences between scholarly and popular sources.
