I fail to see how the situation is any different for a 40 year old than for younger junior devs who either get education or self-educate and start coding.
I think the most important thing is to accept you can never stop learning.
Agree playing around is a good idea :)
Aka the things you learn at that young age are nearly impossible to learn when you're not young anymore.
There are some things you can learn only as a child. Those differences become apparent only with feral children who fail to adapt to society at later age.
Programming languages and frameworks are created as tools for humans. You are never too old to learn to use tools for pragmatic use cases.
Also, feral children may not be a relevant example as they have not undergone the full childhood development and in that sense they have a development disability as opposed to just having missed some typical learning. They cannot learn some typical human things and the rest of us cannot learn some typical unhuman things.
And yes, I agree on your assessment of them.
The canonical example is fluency in an unfamiliar (spoken) language. Most people lose the ability to internalize a new language to the point of being able to 'think in the language' as opposed to 'translating in your head' past their tweens, although the skill of deliberately acquiring new languages is itself learnable, and of course improves with practice, but the ability to learn to speak a language 'natively' (not merely fluently) is lost by nearly all people even earlier.
However, more to the point of this discussion, this age-linked loss of ability or plasticity does not seem to apply to learning programming languages (it is fairly common that one's first programming language is successfully acquired well past that point, after all). I suspect this has something to do with differences between listening/speaking vs. reading/writing fluency.
The fact that at least some older adults do internalise new languages and become undistinguishable from native speakers begs the question why everyone cannot. I'd say plausible explanations include adults being buzy or lazy with their lives, having a fixed mindset towards language learning, bad pedagogy etc. as alternatives to loss of the necessary plasticity. All these can apply to learning programming likewise.
Sure you won't pick up a language from mostly just hearing it like when you were a little Hans but you'd be surprised what you can learn when you're not "young" anymore, whatever "young" means.