I got it around 36, and coincidentally a friend 5-6 years younger than me in a different part of the country got it at the same time.

My research at the time led me to the same conclusion: Since we've basically eradicated chickenpox, we're not exposed to the varicella zoster virus as much as previous generations (via children that have chickenpox). Without exposure our antibodies / resistance fade out.

Since we had chickenpox, the virus is already in us and dormant. When it wakes up and decides to do its thing, our bodies have forgotten how to fight it effectively compared to previous generations - and as a result, the incidence of shingles is increasing in younger populations compared to previous generations.

My doctor said vaccination for under 50 is only indicated after multiple occurrences of shingles... so here's to hoping I'm good til the guidelines change.