Older people are boring because the things that matter are off-limits to discussion. They're too sensitive, and also generally pointless since you can't change past decisions, and can't easily untangle present commitments, so introspection and careful reflection aren't always actually in your best interests.

The 'busy' thing might be because they've taken on more responsibility at work. As much as it sucks being the junior person at work and being dumped on, leadership positions are worse. Money is better, but managing people can suck. The drama and pettiness and rivalries don't stop with high school.

Or, TLDR - older people just suck in different ways than younger people.