

“Less” is correct. “Less” had been used synonymously with “fewer” to denote countables for centuries before the contrivance of a distinction, and that usage has continued on despite some’s insistence of one.
Unless you are writing in some professional or technical sense that demands “fewer” instead, “less” is fine.



The language is ancient, but, since it has continued to be used long past its ancient origin, words and phrases have been coined in later periods for various purposes.
Also, the “early modern” era is roughly considered the period between the Middle Ages and the Industrial Revolution.