Guillaume Dumas, a 28-year-old who attended classes at several campuses, including Yale, Stanford, and Brown, for free (Guillaume Dumas) If you want to start taking classes at an Ivy League university unenrolled and undetected, says Guillaume Dumas, a 28-year-old Canadian, start with big lecture courses. If you must sit in on a smaller seminar class, it’s important to show up consistently starting with the first session, instead of halfway through the semester.