My local community college offers free credited classes to senior citizens, as long as a class is not filled. They don't even charge a registration fee. One can audit a class for no credit or opt to earn credit. As a bonus, one can get student discounts some places if you are enrolled & have an ID card. In my community, continuing education (non-credited) classes are not included in this free deal... (click title for more info)
... But it pays to ask because different areas do this differently. Some areas consider seniors to be 62+, others 65. A 70-yr-old woman in the last class I took was ready to earn a graphic-design degree & had not paid a cent in tuition, paid only for books and supplies.