The only thing I have is CAA (U.S. equivalent is AAA) . That said, I'm also 71 years old. Whenever I travel I always book online. I click each box to see what the discounts are and generally they're all the same and not cumulative. I've often checked the AARP box (despite not being a member), the discount is applied and nobody has ever questioned it at check-in.

All that said, looking at the cost of membership I think you'd pay for it with the savings from your first hotel stay, not to mention the other discounts!