We liked the aquarium at the Mandalay Bay.
DH and I took a flight to the Grand Canyon. Seeing all the canyons from the plane on the way there was amazing! I had ulterior motives - I wanted to visit the GC with our kids but DH wasn’t too excited. Once he actually saw it, he agreed we should come back with the kids. 
Lots of great shows. Definitely do at least one Cirque show. Raiding the Rock Vault is a show in a really small theater with a rotating cast mostly of musicians who were in big name rock bands in the 70-90’s. Im a bit younger than you, but it was a great nostalgia show for me and I think probably for someone 60 it would be as well.
Go downtown one night. It’s a bit of a circus, but even if it isn’t your scene it’s still an interesting place to spend an hour checking it out.
When you go downtown, get a reservation at the Laundry Room if you and your husband drink alcohol. It’s a very small speakeasy, and I had some of the best drinks I have ever tasted there. No wine, no beer. A very large drink menu, plus bartenders who are excellent at making a custom drink for you based on your tastes. Google it. Very worthwhile in my opinion.
Thanks again for the excellent suggestions. For once not waiting till I get there to decide what to do!
We took a helicopter ride that took us to the Grand Canyon and over the Hoover Dam.
Loved watching the Bellagio fountains.
See shows and eat well.