Shingles is caused by varicella-zoster virus, the same virus that causes chickenpox. Historically, most people got chickenpox as children and then shingles occurred in a small proportion of patients as they got older (over the age of 60, or if their immune system got suppressed due to disease, chemotherapy, etc.). The US recommendations for receiving shingles vaccine (Zostavax) are to receive it after age 60 based on this historical pattern. 

However, in the last decade, the age of onset of shingles has been decreasing . No one knows why, but it is of major concern to both primary care physicians and ophthalmologists. Shingles can cause persistent, severe pain on the skin, and can cause vision-threatening inflammation and damage to key tissues of the eye that are difficult to treat or recover from.  

Hence, I am going to recommend that everyone consider getting shingles vaccine over the age of 50 (unless they are actively immune-deficient, on chemotherapy, are allergic, or have some other contraindication).  If someone is going to be on long-term immune-modifying therapy (biologics for arthritis or lupus or Crohn's disease, etc.) or is a smoker or has a prior history of leukemia or lymphoma, I am going to recommend that they consider getting the shingles vaccine at age 40.  This decision should be discussed with your primary care doctor, but shingles is a bad disease and if it can be prevented, let's do it!