I'm 42 in Canada and just got the first shot yesterday. Doctor prescribed it because I'm getting psoriasis and I guess that puts you at a higher risk of developing shingles. With the prescription, it was fully covered.

Presumably if you were vaccinated as a child against chickenpox (Herpes Zoster) and didn't get chickenpox then you already have the protection.

There are no dementia statistics versus vaccination for that demographic because vaccination started about 1995.

There is also a relevant XKCD: https://xkcd.com/1950/

If you are thinking that dementia is caused by shingles, then also consider that shingles is caused by chickenpox.

Why not?

fly to a 2nd or 0th world country and pay a doctor to do it