Great thread, but ten years old now. I play at assisted living residences and "memory care" units regularly. PalJoey here has great advice, and your list looks good.
If they're 80 now, they were 20 in 1958. Elvis, Doris Day (Que Sera, A Bushel and a Peck) and young Rock and Roll, including things like Love Potion No. 9 (1959).
Sing-alongs like Side By Side, You Are My Sunshine, What a Wonderful World
Broadway standards are still the best. Try some from Annie Get Your Gun, including the saucy Doing What Comes naturally.
Blue Skies, O What a Beautiful morning, Bye Bye Blues, Bye Bye Blackbird, Zippedy Doo Dah...
I like to close with Happy Trails (Dale Evans).