always look on the bright side of life

"Can still do most things reasonably well" Jesus you're 45 not 85

Spoken like someone in their 30s at most lol
Ok doc, what do you suggest? I'm 40 and somehow my 80 year old mother has better mobility than I do. I can't even tell you why I have pain, there is no injury. Doctors can't tell me why. I've tried everything short of opioids and back surgery, and I know those aren't going to help either. What the hell do you do when your body just doesn't react normally to exercise, stretching, physical therapy, etc?? It's not that I want to accept that this is my life now, but there don't seem to be any other options. Just be glad this isn't happening to you, I guess.
People with 50 behave like they are 80

I'm 25 and I'm deaf, can't sleep, can't eat, everything hurts, hands don't work, and fucking wheat is trying to kill me. But hey, at least my dogs are adorable little idiots and I'm about to move somewhere much safer and happier (where water actually falls from the sky) with my best friend.

I could still do without the knee pain though.

Do leg stretches every day. Most knee pain is associated with certain muscles overpowering others in rest state. Stretch them out to reset that balance. It's worked wonders for me, started seeing results in ~2weeks.
- My knee pain is associated with arthritis, unfortunately. I wish stretching helped. I'm even a couple years younger than OP, but when I walk up stairs it sounds like I'm crinkling two big balls of cellophane.
- Any specific stretches you can recommend?
  
  My knees have been weak compared to the surrounding muscles all my life, and now that I'm in my 40s and overweight, that's really taking its toll lol
Amputate your legs, no legs no pain!
- Phantom pain would like a word
- Until the phantom pain comes along (it's a real thing! Wikipedia)

It’s the aches and pains that really wear me down.

Most of the aches and pains related to "aging" are significantly alleviated by reducing your total body weight. Especially in America, where 2/3 of us are overweight or obese.

Most of losing weight is diet not exercise.

So, study some nutrition and cooking, eat better, go on walks and do some pushups, and you'll be more fit in 3-6 months.

Thanks for coming to my TED talk