9th -12th grades (age 14) and up. Do not let the fact that it includes some college-level lectures mislead you into thinking it is not for high-school-age students beginning in 9th grade–it is designed for them. Dr. Mortimer Adler long ago (beginning in the 1920’s) noted the decline in American education, and proposed a return to the study of the Great Books and the Socratic (conversational dialectic) method of studying them as two of the major parts of the remedy. He also noted, over many decades of observation and experiment, that teenagers, after the substantial completion of their education in the learning/liberal arts in elementary/primary school through 8th grade (learning reading, writing, speaking, listening, calculating, problem-solving, observing, measuring, estimating and exercising critical judgement), are thereafter able to use those skills to study and profit from the study of the greatest books and the great ideas contained in them. We have an extensive article on this point HERE. This clearly holds for excellent, well-prepared lectures, such as the Great Courses lectures, as well–lectures taught by enthusiastic, great teachers can obviously add much to a student’s learning experience. There is no point is reading books or listening to lectures that we fully understand and which do not stretch us intellectually.
The corollary in that it is a waste of the time and minds of teens not to expose them–not to familiarize and acquaint them–with the greatest works and most profound ideas. “Learning, neglected in youth, loses the past and is dead to the future” – Euripides.