You might want to update your information.  For example, the AARP has many different branches with many different tax structures.
-AARP Foundation, a 501c3 non-profit charity that helps people over age 50 
-AARP Services Inc., a for-profit corporation that provides quality control and research
-Legal Counsel for the Elderly, a 501c3 non-profit charity 
Etc.
If you think the AARP is not a non-profit then I direct you to what is linked to in the same wikipedia article I got the above.
http://www.thenonprofittimes.com/wp-content/uploads/2015/07/8-1-15_Top50PI.pdf
As to regards of income, like Trump, the money comes from the brand.  "While AARP is not an insurer...it does allow its name to be used by insurance companies."
Royalties for the rights to use AARP's intellectual property ($838,649,000) vs. Membership dues ($295,180,000).
https://en.wikipedia.org/wiki/AARP
Putting aside the conservative bias in the American Thinker, one should always be wary of cherry-picking information.