Ecclesiastes is, indeed, one of the three books attributed by Jewish tradition to the tenth-century-B.C.E. king Solomon. The rabbis believed he wrote the exuberantly romantic Song of Songs as a young man, the wise and reflective Proverbs in his middle years, and the gloomy Ecclesiastes in his old age. Today, few scholars accept the attribution of the book’s authorship to Solomon. For one thing, Ecclesiastes uses words that were unknown in Solomon’s time. For example, pardes (see 2:5), a Persian word meaning both “grove” and “paradise,” first became known to the Jews probably no earlier than the sixth century B.C.E. Finding it included in a work supposedly written four centuries earlier is as jarring as it would be to find the word “Lexus” in a sonnet attributed to Shakespeare. — Rabbi Joseph Telushkin, Jewish Literacy, Pg 99
If this is true, what are the chances of there being other books credited to the wrong person? This certainly makes one think about that possibility.