I have been a member of the AARP for several years as they often have good tie ups at Hyatt, my hotel chain of choice. Membership is available for both US Residents as well as those of us living abroad who are over 50 years old. The fees do vary significantly and non-US members can only join for a year at a time. Current rates are:
AARP offers a range of discounts on travel. However, many of these only work for those living in the US. For example the discounts for British Airways and via Expedia, don’t work unless you have a US credit card. There other discounts for car rentals, cruises, Cirque De Soleil and UPS which seem to work for non-US members, although often only at US locations.
The major benefit is having access to AARP rates at leading hotel chains, with properties from 5* on down. A sample of the higher end property discounts are:
A couple of worked example for Hyatt to give you an idea of the discounts on offer and how to obtain them. Hyatt makes it pretty easy to search for the AARP rate, as it is an option right from their homepage.
A search on the Grand Hyatt in New York in December offers these rates:
Not every room type is offered for the AARP rate but there is a reasonable choice, although if you are looking just for a basic room, the Advance Purchase rate is still cheaper although it cannot be cancelled or amended.
I like using AARP rates as they often come with the same cancellation policy as the normal Hyatt rate as well as earning Gold Passport points.
At Starwood there is a special search page (here) which gives access to their special AARP rates. A search on the W in San Francisco, again in August shows the AARP rate as $311, the pre-paid rate as $326 and the Flexible rate at $346, so a saving of about 10%.
A search for London showed no hotels with the AARP rate in May, so it seems less available in some locations.
A check of Best Western properties in San Juan, PR revealed a discount for AARP equal to that for AAA members at 10% of the Best Available Rate.