E.g., the Shingles vaccine simply hasn't been tested in <50 populations. But if you're under 50 and you've had the chicken pox, you should ask your PCP to prescribe the shingles vaccine off-label and go get it, because shingles sucks and the vaccine definitely works.

I don't follow your logic here. The GP comment is saying that the vaccine isn't available for populations it hasn't been tested for. Why are you recommending people ignore the fact that safety and efficacy testing isn't available for their population?

And how can you say the vaccine definitely works for populations it hasn't been tested on?