My stepfather's father became addicted to pain pills (not sure what type) in his late 50s. He was about the furthest thing from the "typical" addict character you can imagine. But, a doctor prescribed something and "bam"...there you go. He was living in AZ at the time and going across the border to Mexico to get double fills on his scrips. It didn't come to light until he was hospitalized and forced back to his proper dosage.
I wasn't directly involved in this, so I have little to offer other than, yes, it happens.