It depends on the kid. If they want to then it is not too early.
We sometimes visited if we were in the area of the country for something else. Not official tours in middle school, but they were aware we are in this city with these colleges and may walk or drive by campus. D21 went on several tours with S19 tagging along early on. Sometimes she hung out in the student union studying and honestly got a better vibe for things than we did on the tour.
We never forced tours but made them available. There were also museums or events they wanted to go to that were on college campuses over the years. Early on we went to see Big Al in Wyoming at the request of the seven year old version of S19 - great museum! Allosaurus Exhibit | Geological Museum | University of Wyoming