I joined when I turned 50, as more of a lark.
Humble brag incoming.
See, as I approached that magical birthday, I received one of their mailers extolling the virtues of joining. All for $12 a year! I was about to toss it in the trash, and then I noticed a tidbit that the spouse of a member automatically received a card.
So, I went online, created an account and paid the $12 bucks. Put in my name, and put in my wife's name for her free card, then sat back and waited,
A few weeks pass, and I get an envelope with both of the cards. Wife comes home from work, and I tell her I have a surprise for her. I take the AARP card with her name on it, and hand it to her. She has a horrified look on her face, and starts to ask "why?"
She was 37 at the time.
Handing over her AARP membership card to her, at that age, was worth the yearly membership. We still joke about it to this day. And she actually has used it a time or two on hotel room reservations, when the AARP discount was greater than the usual discounts either of us receive.