So, on the "bad examples". The reason us old dudes get paid more despite being slower, costing more to health insurance, being grumpier (this goes along with it 100%*), maybe being not as fun at the company's events--- is---
We have done just about everything wrong that could possibly happen in our jobs (and lives) by age 50. We have also done a lot of stuff right. The "experience" that you gain in life is learning from your mistakes and successes. This doesn't mean mistakes stop when you get older, you just make more careful decisions by default and less mistakes.
*The grumpiness comes from when you're forced to watch someone else repeat your mistakes, despite repeated warnings... trust me on that....