Drink beer with my dogs.
You people are gross. My favorite hobby - putting off until some nebulous future time what would be better done today :p.
Other than that - on the sedentary side reading/research, computer games, music, wasting time around here and of course the always reliable boob tube( and its myriad cousins ). Less sedentary - nature photography/bird watching/nature stuff in general. Always good to get at least one less sedentary hobby in there.
But for goodness sakes only default to being productive when it is the last thing left on your list ;).
And getting out and going to a gym does a lot more for some than simply getting their blood pumping faster and burning calories. It can be a vibrant social setting where friends are made and good times are had working out (sometimes that just consists of working out the jaws, tongues and lips lol).
I’ve learned to make a to-do list only for that specific day. New one every day. Make it a mix of practical, boring, fun, etc. things. Bake and cook. Read and organize. Pedicure and gardening.
Start going to water aerobics at your local rec centre. It’s chock full of women your age and you’ll soon get to know many people.
+1 very good idea
Reading actual books made from the finest of dead trees.
snob 
Ugh, you mean those people who block three swim lanes so they can bounce around in the 4’ section for an hour and a half? What was wrong with just playing cribbage and sneaking gin into your tea, which bothered no one and took up only a table nobody was using anyway?
If you have 182 hours to spare, you can watch the entire Marvel Cinematic Universe (about five hours fewer if you skip The Incredible Hulk and 5X through Iron Man 2 and Thor: The Dark World). If you don’t have that kind of time, watch a fifteen minute summary and then just watch The Avengers, Captain America: Winter Soldier, and The Guardians of the Galaxy films, then fall asleep watching Thor: Ragnarok and wake up completely confused as to why Jeff Goldblum is in drag.
Stranger
Mix champagne with slim fast. That sure passes the time.
At first I was thinking of Slim Jims, which apparently "pairs well with charcuterie, like Sicilian Nero d’Avolas, red blends from France’s Languedoc-Roussillon, and Spanish Monstrells."
I picked up a Rogue lap steel guitar cheap (it’s surprisingly decent for a mere 80 bucks) and when I’m alone I plug it into an amplifier and attempt to maim a few tunes. Thanks to youtube, I can now crank out an almost decent rendition of “Sleepwalk.” Doesn’t even require the build up of any fingertip calluses. And much more fun than doing things that make me sore and sweaty.
Yes, precisely those people. Did you ever notice what a good fucking time those people always seemed to be having? For some people, the main health advantage of taking part in such an activity is simply getting out and moving and socializing and having fun with people they otherwise wouldn’t ever even meet. Keep in mind, the OP says she’s 61, an age that seems to be about what I would peg most of the ‘wear water-floaters and bounce around vaguely for hours class’ participants.
As long as they are not of the undiscovered country.
Hey, are you calling out SoaT’s hook? He’s just being human. In fact around here, he’s man of the year. Everyone’s hero, even. Good morning, Vietnam.
Either reading, or Second Life.
Help others. Your life will become messy and interesting right away. Best if you can combine this with a spiritual practice of some sort, to deal with the messiness.
Tons of good ideas above.
One of my favorite all-alone activities is cooking, but for this to work you need a place for all the food to go. Homeless shelters or friends with teenage boys in the household are good options.
I just picked up a lap steel myself (an old Harmony). It’s so much fun, I’ve been neglecting the guitar (and mandolin, harmonica, tiple…)
What about taking an online class on Coursera or edX? I took a few while I was trying to figure out whether to return to school or not. There were people from all over the world on the message boards. It was pretty interesting.