Is Granada too hilly for an 87 year old

There is certainly plenty to do.
The city center is flat.
There is a bus that will take you to the AlHambra. You ned to buy tickets in advance online to be sure of access. Make sure to use the official ticket site, not a third-party site, for tickets.

Cordoba is flat and would be a lovely 2.5-day stay.

There are red buses you can use to get up to the Alhambra from the town. But be warned we were packed in like sardines. I am sure you could get a seat, given his age and depending on what time of year (although this was September). I would tell you to get a hotel with good A/C and make sure you don't go in June/July/August - just too hot.

The Alhambra and neighboring areas are on a hill. The Alhambra is not that difficult to get around once inside the grounds.

Granada’s little Morocco, cathedrals, Silk Road are flat. There may be some inclines but we’re not significant. I suggest taking a cab if you are going to the Alhambra. Maybe look at some YouTube’s of Granada so you two can better assess its terrain.

Taxis are relatively inexpensive and plentiful. We used them this past November to get up to the Alhambra and the viewpoints. Our hotel called them for us and they arrived in 2-4 minutes. We either walked or took taxis downhill. Buses are also an option, and the routes to use are in the RS guidebook. I think you will be ok if you make use of these options for the hilly areas.

Just take a taxi to the Alhambra. It can get you all the way to the top.

I took a city bus there and back to the Alhambra. It’s doable and the buses are easy to spot. I would suggest staying in the city centre for accommodation as it is flat.

I agree with Carol. Take a taxi. From memory I think it was only €5 - €10 Euro across the city and right to the entrance. We used the Pidetaxi app, or if you're leaving from your hotel you could maybe ask them to call a taxi for you (likely slightly more expensive).

We took a taxi to dinner at Las Tomasas with it's beautiful terrace but walked back to our hotel. It was downhill nearly all the way but very dark so we used our phone's flashlights. Also my shoes had some glow spots that helped. We're very agile near 70 year olds.

Especially if it is rainy in Granada, I encourage caution!

Wandering back from the Alhambra on a rainy day, I fell on some very slippery steps and sprained my knee. (Despite walking very slowly and holding the rail.) A non-helpful guy who saw me fall shook his head as if to say "well what were you thinking to be on those steps in the rain anyway?" Point taken. Bless the heart of the local pharmacist who got me back on my feet and saved my trip.

The asphalt streets were fine. But I found the areas paved with river stones and mosaics, as well as the steps, to be slippery. Even near my Granada hotel-on-a-flat-street, the pavement stones were slippery.

Obviously, this could happen in any city, on any hill or steps. So I'm not discouraging Granada. A taxi or bus or Uber up and down the hills might be a good investment.

Also wanted to add that the Albaicin neighborhood is wonderful and has many stairs (as opposed to sloped hills), if that makes a difference.

We did the Alhambra about 12 years ago, we were in our mid-60s then. We did it just fine.
I seem to remember that the Alhambra tour was quite lengthy and took hours because it included places outside the Alhambra.
There were no hills on the tour, but there were going up to the site.