Middle age is generally not defined as 50% of your life expectancy: https://en.wikipedia.org/wiki/Middle_age
Physical? I can feel and am acutely aware I just can't do what I could 20 or even 10 years ago. No more all-nighters for me, my body just can't take it. No more high speed action games for me, my body just can't respond fast enough.
Mental? My memory is noticably declining, and my ability to learn new things is significantly deteriorated from my prime. I find myself clinging to stuff I already knew because they give me some sense of familiarity and safety in an increasingly alien world.
Social? I've stopped bothering to actively make new friends or otherwise socialize, I just can't be bothered anymore with all the hassle that human relations entail.
If I were to describe my current phase in life as the four seasons, I'm in autumn.
I can no longer just learn the syntax for how the pubsub works, I have to stop and think how to build an architecture around it, how to create an abstraction for my use case, can it be integrated with Postgres triggers etc.
I get frustrated nearly daily at my mental decline. I was always a math wiz who could basically do up to precalc in my head. Today, I have trouble carrying numbers doing basic long multiplication. Worse, I have trouble finding the words I'm looking for when writing.
Autumn feels optimistic. I don't know what the future holds, and maybe I'm being dramatic, but it feels like Winter. I feel like my body and mind greatly betrayed me in my 30s.
It should perhaps better be described as a mid-life-expectancy crisis.