It's from chronic exposure to lead, especially inhaled lead from leaded fuel combustion before it was outlawed, or heavy industry in urban areas back in the 1980s.

Gen X are already worse than boomers, when boomers were children cars were far less common so lead exposure during early childhood was far lower than Gen X.

Millennials only had high exposure to lead during childhood.

Gen X had high lead exposure their entire lives.

The worst part, all those cheap disposable vapes that gen z are sucking on contain lead in the solder which when heated releases fumes, so a lot of gen z will be the same when they get to their 40s,50s

But I have hope for gen alpha, the ones that do vape get bullied by their peers for it.