Admission officials do indeed like to see that students have challenged themselves, and this often includes taking college-level classes while still in high school. BUT . (and I bet you could tell that a "but" was coming :) ), not all college classes are created equal. At some community colleges, the calculus class may not be as demanding as a high school AP course. Admission officials may, in fact, wonder why your son took this particular class outside of his high school. Was he fearful of the high school AP class? Was he not admitted to the high school AP class? So your plan to impress the admission folks may backfire unless it's made clear to them that the college course was selected for its rigor.
Granted, plenty of high school students do take calculus at nearby two-year schools and even sometimes at four-year colleges, but usually it's because they couldn't fit the high school AP class into their schedule or there was some other reason why they were not able to take it at school. (And some high schools don't offer calculus at all.)
Although your college advisor/family friend is correct when he (she?) says that your son may find more interesting and/or challenging classes at the local college, calculus may not be one of them. If he does want to try a college class, and if calculus fits readily into his high school schedule, I would suggest that he choose a different class at the college instead . e.g., something that interests him and that isn't offered at his high school but would still qualify as a "liberal arts" field (e.g, "Introduction to Symbolic Logic," "Archaeology and Prehistory," "Cultural Anthropology," or "Inorganic Chemistry, not "Advanced Document Processing," "Ophthalmic Assisting," or "Firefighter Fitness Training.")
So, bottom line: If your son is excited about doing this class at a community college, I wouldn't necessarily pull the plug on it. But I would urge you to first find out if the college class is as rigorous as the high school class and if it follows a similar curriculum. If your son is applying to highly selective colleges and, especially, to the top engineering schools, he will be "competing" with applicants who have taken the AP exams in Calculus AB and BC and who have earned 5's on those tests. Thus, whether he studies calculus at his high school or at the college, he would be wise to take the AP exam. (You don't have to be in an official AP course to take the test.)
If it looks like the college course won't prepare your as well for the AP exam as the high school course will, then I recommend that he take AP Calc at his high school and try something else that interests him at the college.
Good luck with this, whatever you decide.
Sally Rubenstone knows the competitive and often convoluted college admission process inside out: From the first time the topic of college comes up at the dinner table until the last duffel bag is unloaded on a dorm room floor. She is the co-author of Panicked Parents' Guide to College Admissions; The Transfer Student's Guide to Changing Colleges and The International Student's Guide to Going to College in America. Sally has appeared on NBC's Today program and has been quoted in countless publications, including The New York Times, The Washington Post, USA Weekend, USA Today, U.S. News & World Report, Newsweek, People and Seventeen. Sally has viewed the admissions world from many angles: As a Smith College admission counselor for 15 years, an independent college counselor serving students from a wide range of backgrounds and the author of College Confidential's "Ask the Dean" column. She also taught language arts, social studies, study skills and test preparation in 10 schools, including American international schools in London, Paris, Geneva, Athens and Tel Aviv. As senior advisor to College Confidential since 2002, Sally has helped hundreds of students and parents navigate the college admissions maze. In 2008, she co-founded College Karma, a private college consulting firm, with her College Confidential colleague Dave Berry, and she continues to serve as a College Confidential advisor. Sally and her husband, Chris Petrides, became first-time parents in 1997 at the ripe-old age of 45. So Sally was nearly an official senior citizen when her son Jack began the college selection process, and when she was finally able to practice what she had preached for more than three decades.