If you can do a sub 4-hour marathon and have good prior trail experience, you should be fine. (You don't have to run to do the down/up South Rim effectively, that's just my fitness guideline).
If you can generally just keep up a solid, motivated walking clip both down and up - not even running - it's just a good fun day. I did it with my mom when she was around 60 y.o. (though she was far from an average 60 y.o.).
December can make it interesting. It's good because you don't have to worry as much about heat and hydration. I did it in winter as well. At the top you can have snow and ice, and it can feel like you're heading off to an arctic expedition. But then it doesn't take very much descent at all before the temperature can go up by 20F or more. But the top sections can be icy. I brought lightweight microspikes to put over my trail runners for the first couples miles down/last miles up. You might not need them - all depends on the timing of snow storms.
Start early. Have smart clothing layers. Have hydration and nutrition plans. Don't make dumb decisions along the way. Good to go.
If you can generally just keep up a solid, motivated walking clip both down and up - not even running - it's just a good fun day. I did it with my mom when she was around 60 y.o. (though she was far from an average 60 y.o.).
December can make it interesting. It's good because you don't have to worry as much about heat and hydration. I did it in winter as well. At the top you can have snow and ice, and it can feel like you're heading off to an arctic expedition. But then it doesn't take very much descent at all before the temperature can go up by 20F or more. But the top sections can be icy. I brought lightweight microspikes to put over my trail runners for the first couples miles down/last miles up. You might not need them - all depends on the timing of snow storms.
Start early. Have smart clothing layers. Have hydration and nutrition plans. Don't make dumb decisions along the way. Good to go.