Am I alone in this? Has anyone else experienced something similar? Or different? Does anyone have some answers?
You are not alone in these concerns.
However, any answers anyone may provide would ultimately prove to be answers specific to their own variations of these questions.
And that's about as generic a solution as possible: you have your questions, answer them.
...
As unhelpfully self-evident or quasi-tautological as that may seem, it helps to consider it as a reminder instead of a solution.
A reminder that your answers can be as fantastical or practical as you'd like them to be; a reminder that the answers you come up with need not be based in some widespread consensus; a reminder that the 'coming up with answers' part is as much a solution as any answer you may eventually settle on.
As an introvert myself--often sharing in your experience of anachronous school-day dreams and the anxieties of aging in isolation--I find the exercise of creation and the community that it tends to cultivate to be the most effective remedies.
Of course, these aren't remedies for the concerns themselves (neither the dreams nor the helplessness of aging); rather, they are remedies for my inability to cease obsession over them. Simply put, they are effective distractions.
(As the parent lives on in their children, and the artist lives on in their work, the restless live best in effective distraction.)
And, for what its worth, my perspective on death is that I'd much rather it catch me by surprise, while I'm effectively distracted, than me counting each day spent as but another step toward its inevitability.
...
tl;dr: immersive distractions, particularly of the creative kind (producing artefacts as 'ideal children') that allow one to channel ones past into the present with future-potential, offer a decent home-remedy for existential angst; at least, that's the change in my pocket.