They call themselves a "non-profit" 501(c)(4).
"AARP is a membership organization for people age 50 and over and operates as a non-profit advocate for its members and is one of the most powerful lobbying groups in the United States....
According to AARP's 2008 Consolidated financial statements, AARP Services Inc. was paid $652,000,000 in royalties from insurance companies that sold products referred by AARP.
AARP also received an additional $120,000,000 for the advertisements placed in its publications."
wikipedia
https://en.wikipedia.org/wiki/AARP