It would be interesting to see a breakdown of why older devs get less awesome over time. I can imagine a variety of causes:
- Slower learning due to reduced brain plasticity.
- Early stages of dementia.
- More poorly rested due to kids, age-related physical discomfort during sleeping, or obesity-based sleep apnea.
- Reduced focus on career development due to getting comfortable and/or responsibilities outside of work (child-rearing, etc.) This includes less time on evenings / weekends to self-learn new technologies.
- Reduced exposure to new technologies, because they're now so expensive that employers only want to pay them to work in their current niche(s) of expertise.
- False perception that they actually are less awesome. E.g., they write half as much code as before, because of a better idea about what's a waste of time.
It's about staying on top of your skills and never assuming you know enough. Always be learning. Most older devs that I know that started sliding into irrelevance did so because they didn't keep up on that.