[gary17the]

From my experience, the "common assumption" that your brain works best only when you are in your 20s or 30s is a complete and utter nonsense. You might get a bit more burned out with time or simply become less passionate about technology in itself or professional careers in general and instead care more about your real-world life, but if you keep your body in good physical condition and keep pushing your brain, you only become more efficient and faster at programming every year, due to your accumulated experience and improved intuition. (Consider the Linus Torvalds guy.) It is only the corporate environment that actually forces you to switch to managerial responsibilities.

[solardev]

It's not just management. Neuroplasticity, from what I understand, can indeed be affected by your lifestyle (as you implied). But there's also the changing demands on your time. Many people are single or casually dating in their 20s and 30s, and have evenings and weekends to spend learning new things or playing with side projects. Then family and kids roll around, aging parents to take care of, eventually your own health issues... the demands of midlife and beyond will compete for your time and attention and leave many people with fewer resources (time, energy, money) to spend on intellectual gratification.

People like Linus are the exception rather than the rule, I think. Stallman maybe even more so? Sometimes I envy them, and sometimes I wonder how happy and balanced the rest of their lives are (maybe they're perfectly happy? I have no idea).