>... then changing companies frequently is good, but only up to some point. Past that point (I would say, 30-something) ...

I know multiple people that have changed employers every couple years throughout their thirties. Each time it was a better deal. There's absolutely no reason to settle in at a particular company just because you're old. To hell with long-term trust building, either a company empowers its senior talent to get shit done regardless of their tenure there, or to the company's own detriment it doesn't.