This subject comes up every once in awhile, and it is good to remind folks they are eligible for a lot of discounts that are little known.
It's not just seniors.. if you have a blue placard, ADA pass for your car.. you are eligible for the "Golden Access" pass from the US government. You get 1/2 price camping in FS, BLM or Corp of engineers parks, and free entry into national park with camping discounts as well.
Pick them up at any Forest Service ranger station. Bring your ADA paperwork and pass.