How do we know how well we're aging?

How do we know when to slow down? Your body will let you know.

It feels like you are obsessing about all of this. I am 90 years old and I just "go with the flow." Listen to your body. It will let you know. I am always told I do not look like 90. My question is: How is 90 supposed to look? There is no answer to that question. The problem is that other people have preconceived notions of how people should look. I am healthy. Unhappily my husband died almost 4 years ago after a 62 year relationship. But I am still living in our house and I have no problem taking care of myself. I do not have to take a lot of drugs, which I really think do more harm than good. I drive. I am independent. I am capable of making my own decisions, be they medical or financial. I attribute all of this to living a healthy life style. I was a race walker for many years. I never smoked. I rarely drank. Fortunately for me I do not have a sweet tooth so didn't eat a lot of sugary things. So, again, I say do not obsess with when you should do what. Just slow down and listen to your body.

I loved the question, but we don't age the same. For instance, you have diabetes and I don't. My life is spent exercising (walk 4+miles each day), eat healthy eating (close to the Mediterranean diet), socialize often, learn new things and sleep as well as I can. When I was in my 40's I swam competitvely. I competed in our state's senior. As the older age groups competed there were fewer and fewer swimmers. But there was one 80+ year old man.
I think we slow down but don't have to quit. Just keep going on.

This question has been on my mind for several days now, focused in part by my back and hips after carrying a 12' 4x4 a few hundred feet. It has taken several days to recover from the muscle strain, something that would have been insignificant 10 years ago.
Add to this, intermittent vertigo over the last seven months and a gain of about 20 pounds over the last two years.
Because of the vertigo I've been walking less and on less challenging terrain. I did a hard, log walk ten days ago and it took me about 5 days to recover. And it was a lot easier to climb hills when I weighed 20 pounds less.
So that's the tough stuff.
The other side is that with wise caution I can regain much or all that I've lost.
-Yesterday and today I increased my walks, but not so much as to have extreme muscle pain after. I can use my iWatch to track my walks so I maintain reasonable effort, not too much or too little.
-I'm back on the Mayo Clinic Diet which worked beautifully for me 3 years ago. In fact I've continued with the diet food choices, but gained weight from eating too many good things.
-I feel comfortable that I can maintain the return to earlier habits.
-I think I need to be more aware of the demands that my choices make on my energies (carpentry, weed whacking, community work) and make sure that I retain time needed for self care and awareness.
-I need to walk early in the day, before the heat.
-I'll track this for a month and see what happens.

Am I aging well?
I know it when I look back my last 2-hr, my yesterday, my last year and can say to myself: Good for you, you have been able to spend your time on What MATTERED YOU Most.
It is the Reason for living of my life-I-want that determines how healthy -- physically, socially, cognitively, spiritually -- I would like to be.

So since for me mental health (and not Physical health) is most important as it helps me get what I want from my life, I aim to be in fit state that helps me to reach what I want from my life.
As one in his 82nd year, I am fit enough to walk all 11 floors in my building, huffing and puffing the last five at my highest level.
My fitness comes from a variety of exertions that promote: strength, speed, stamina, balance. Of course, healthful food and stress management matter too.
And haven't seen my doctor for seven years --, nor had any tests, surgeries, or medications.
If I suddenly died, I would like to think, well, I did get to live what I wanted most from it. a philosopher (Nietzsche?)) has said: We die at the right time.

Back to you: 20 lbs is too much your body is lugging around. Only YOU would know what is the 'Right' weight for you, bc even the BMI table only tells what is 'healthy weight' for a Typical Person. The weight where one feels most Fit, is that is what YOU want.

I can only wish for you -- as I'd wish for myself: May you have an Interesting life. For what is a life if it didn't give us a sense of Aliveness -- of having sensed all its wonders and delights?

I think everyone's tolerance will vary. I'm 81 and worked out most of my life. Here recently, I thought everything was ok. While working out, push-ups, light weight lifting, lat-machine, again light weights. I pulled a muscle in my back. No strain just a normal workout with light weights and push-ups (10). That's been 1.5 months ago. I'm just getting over it. Lesson learned:
You don't have to overwork an old body to get laid up. I have found that in my case, moderation is key. Don't work out every day like a machine. Work out and give your body a rest to recuperate. At 81 that's my suggestion. To pull something and be laid up is not worth the effort. I'm 5'8 and weigh 150 lbs. Sorta skinny. So moderation is my goal. My body demands it. Don't hurt yourself. Remember, everyone's circumstances are different and moderation is key. Also, before I go, listen to your GP.