He advocates for prioritizing your health, do cool free stuff instead of cool non free stuff and do not be too materialistic. The more you read, the more you understand this is not even about saving or retiring early.
He retired early by having a high (but not sky high) income and saving like 50-70% of it.
Nothing he did is unbelievable, you can't apply everything but you can apply a lot and it really gives benefits, no matter if your goal is to retire early or not.
Plus he doesn't sell anything and doesn't fool anyone to earn money. :)
You'll make death come later if you adjust your lifestyle. Sport + nutrition + good sleep = better energy day-to-day and better health -> aging slower.
24 yo here, so I can't answer your question.
BUT. From what I read in your post, you're not only asking if there is a future in tech, you're also saying you're afraid because you don't have as much energy as you used to.
I'd say energy has little to do with age. As every 40yo you probably are 20lbs overweight, you haven't done much sport in the last years, you probably don't manage your sleep as well as you should, same goes for nutrition, etc.
When is the last time you took a MOOC, a new formation, learned a new skill by yourself?
tldr your energy has more to do with your lifestyle than with your age. Gl. :)