Can a person exposed to lead poisoning 80 years ago get dementia from that?

No: As an octogenarian, do not worry about the follies of your youth. Now if you were 90 or 100; well, we'll talk.

Confusing question: Are you asking if someone who had exposure to, not diagnosed with,lead toxicity 80 years ago & remained symptom free for these 80 years would suddenly have dementia from it ? I have difficulty accepting a label of dementia from that with no documentation. We were all exposed to some environmental lead in various forms if alive before lead free paint/gas.