Leaded gasoline potentially affected at most a few generations in the 20th century. Do we see a spike in dementia correlated with the years that leaded gasoline was used?

Just conjecture -- but the ww2 generation would have had the most lifetime exposure to leaded gasoline. They're dying off in increasing numbers.

Subsequent generations may have had less exposure due to suburbanization and the banning of leaded gas.

This was my thought too. From a cursory look at the ages in this study I'm thinking it's not the cause here at least? I may be wrong.

I'm still very curious is Alzheimer's is caused by something environmental? I've heard aluminum suggested but I haven't seen anything conclusive. (And I can't find antacids that don't include aluminum!)