>>We get wise too late...
>>...and old too soon.
>>–Danish Proverb
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At early-forties, I don't think I count as "young" anymore.
Definitely: growing up without a cell phone was beautiful. I still remember driving around semi-lost, using paper maps, quite fondly (I still print directions).
My last partner (eight years my junior) "grew up on her cellphone" and it was just remarkable how fucked her brain was... at least different from my own landlined-childhood POV (e.g: attention-span; need for constant contact).
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And yet, my brain also enmushifies (lately: increasingly).
Forties isn’t old. You might not have the energy reserves of a younger person, but you shouldn’t feel like your brain is mush.
It is questionable what is, at present day, considered young and old (and particularly during mid-forties), as life expectancy doubled last century from roughly ~40 to ~80 years. which makes everyone in their forties old by ... olden standards and mid-life at current ones.
if we get to live through the (forthcoming or already unfolding) singularity, there's a fair chance new life standards extend to 140-180 years*, with medicine, yoga, nootropics** and all.
* https://en.wikipedia.org/wiki/Life_expectancy#Maximum ** https://en.wikipedia.org/wiki/Nootropic