Those things you listed to prove your point can all happen to any of us at age 12, and all of the rest save child-bearing can happen at any age.

All of them are external things that change our situation, sure, but your choice to be "old" or not based on them is still a choice, which was the parent's point.

Conversely, you're young as long as you believe you have control over imperfections.

Last year, I slipped in a puddle on my bike. Last week, my orthopedic surgeon told me I can never be a runner again. There is too little cartilage left in my ankle.

Yesterday, Strava told me I logged my 250th entry. Scrolling down my activity stream past the walks I logged recovering from my ankle injury, I saw the hundreds of runs I went on when I took jogging seriously. One of those runs is now the best run I'll ever do.

Not being able to run is an imperfection that is "permanent" and that I will never "grow" past regardless of how much I care to do so. That's what getting old feels like.

I couldn’t run, I sometimes couldn’t walk. People used to think I was a personal trainer because I was so fit. Diagnosis was 5 years ago.

Went through grief/trauma getting diagnosed with arthritis.

Now 5 years later, from just walking shorter distances more often and processing the grief, I’m back at the gym and started soccer and ran for the first time in ages. Felt very weird but I just work within my limits. I also cycle at least 30 minutes of intense cycling 6 days a week.

You’ll learn to adapt and adjust, it does get better, you just have to become a child again and approach it differently.

I ultimately will still need joint replacements at some point in the next few years, but I’ve had a complete mindset shift. My current goal is to become even fitter than my previous state.

I agree, there is a big mindset shift needed to make peace with our body not being entirely under our control. To me, that mindset change is a big part of what it feels like to not be young.

If think of a lifespan as an arc, it's something like:

1. In early childhood, you are gradually mastering the physicality of your body. Learning to control elimination, getting more coordinated, learning physical skills, etc. I think of it like learning to control a sailboat, harness the wind, operate the sails, etc.

2. When you hit young adulthood, you're at a sort of peak where your body can be an abstraction. You can do what you want in the world without having to worry too much about your body getting in the way. At this point, you are a skilled sailor on the open ocean.

3. Then as you get older and/or unlucky, things outside of your control happen to your body in ways that materially limit your own agency. You may want to do X, but your body means that's off the table. You can still do Y. Now you are navigating shoals. You can still control the sailboat, but there are rocks there and you must navigate around them whether you want to or not. Some places simply can't be reached anymore.

4. I'm not there yet, but assume that as we age, the number of rocks increases and we increasingly focus our attention on the sailing we've already done in the past and make peace with our limited journeys going forward.

That first time you crash into a rock and move from 2 to 3 is hard.