Age is definitely a protected category. I don't know how 55+ communities get away with it, tbh.

There are also different rules depending on whether you are a landlord-owner-resident or a landlord who doesn't live in the building. Most building over 3 units have stricter requirements, too.

Here's some detail.

The employment* and public accommodations statutes prohibit discrimination based on race, color, sex (including pregnancy and sexual harassment), disability, ancestral origin, religion, sexual orientation, gender identity/expression and age. The credit statute, in addition to prohibiting discrimination on these bases, also prohibits discrimination based on marital status, familial status, military status, and association with members of a protected class. The housing statute covers all of the previously mentioned areas in addition to status as a victim of domestic abuse, housing status, and lawful source of income.

http://www.richr.ri.gov/about/index.php