My husband and I talk a lot about this, probably because he works in healthcare and sees first hand what happens to people as they age, both physically and mentally. Plus, it's not like we're getting any younger with one kid already in college. (insert deer in headlights emoji that I don't think exists, but should...) We're also probably getting more stubborn and stuck in our ways, right?
The solution can be summed up in two words, be uncomfortable. And let me follow that up with, but don't hurt yourself. There needs to be balance. Both of us have been on the injury side, and do not recommend it.
What's being uncomfortable? So many things... For me, I'm pretty introverted, so just having to say my name in front of a large group of people is very uncomfortable. Oh, and please don't ask me to say a few words about myself, heart palpitations... ugh. However, a better example is running, because it makes me uncomfortable in multiple ways (thus having multiple benefits). I run all year long. Not every day, I'm not a robot. And don't be too impressed, my distance varies greatly. If you're going to be impressed, be impressed that I rarely let the weather dictate my running. The photo attached to this little rambling is of my most recent run where sleet was piercing my face. The road wasn't terribly slippery and we have very little traffic, so still safe enough, but comfortable - goodness no. Probably the worst run I've run all year (lol it's January). So why do it? I could workout in the house, or buy a treadmill, or just sip another cup of coffee on the couch and put it off another day... Because being uncomfortable does a hell-of-a-lot for your body and your brain!
Uncomfortable situations push me to overcome them in some fashion. Essentially they make me mentally and physically stronger. If I chose instead to run on a treadmill, for one, I'd be bored out of my mind and I'd probably end up streaming a show while running to nowhere. With my brain not being challenged at all, like where to step to avoid an icy patch, or pausing to smile when the sun breaks the clouds, I'm left putting my brain on autopilot. My body too. Muscles are amazing at remembering movements. Give them the same monotonous movement for 30 minutes a day and they'll condition themselves to do that with the least amount of energy/effort. That doesn't exactly give me the workout I need. I don't need my body to run perfectly efficiently on a treadmill when I'm 85. I need it to be able to react quickly to different terrain, do a variety of movements, etc., and not pull something or worse break something... I'm risking that plenty enough carrying 50 lb bags of chicken feed and throwing hay bales around.
I could still choose not to run in skin-piercing sleet, right? Sure, but choosing to be uncomfortable (safely) for a while does more than just keeps my muscles and mind activated, it gives me a new perspective, a new challenge, tests my character and resolve. Think of a time that you persevered, it felt great (when it was over), right? Gained you some experience under your belt, grew some of that hair on your chest that people are always talking about... it also probably meant you stopped taking something for granted (at least for a bit).
Running in this horrible weather made me reminisce about running in the warm summer sun. It also made me look forward to getting back to the house and enjoying a hot shower, which reminded me that we didn't always have running water. For over a year we used to haul water and heat it on the woodstove for all of our showers. Such a simple thing that I now, again, take for granted. AND, I was reminded that I have a scary-looking neoprene face mask that I should've worn. It has holes in it that make me look like Jason from Friday the 13th. Beauty isn't everything.
There's even a bonus. I've run in snow pants, through miles of mud. I've been lost, seen the cutest porcupine EVER, been chased by birds, stopped and took photos of flowers for 20 minutes... The list goes on. No one has great treadmill stories (that don't involve falling... or their pants falling down exposing their Garfield print granny panties, gosh I hope those exist!). So being uncomfortable makes for great stories to tell your friends.
Good luck to you and all your epic uncomfortable experiences. To your health!