My uncle is 84 and has AARP (not the insurance). He gets some discounts just from having the card. I don't know how much it cost but I don't think it was much. I know he got a deal on his cell phone because he was a member. I guess it's kinda like having AAA for ers and you can get discounts at certain hotels, car rentals, etc type of thing.
I guess I'll find out in 2 years when I'm 50. So far they aren't knocking on my door.