Junkies and some other unsupervised narcotic users, yes, with malnutrition and the ravages of cuts used in smack being part of it. Chronic pain patients? Not unless they are cut off. This was proposed as something diamorphine, morphine and the like could do by 1930 or so . . . when a doctor mentioned this many years ago, I actually was not happy about it -- I'd worked really hard for that pate of silver hair I had by about age 30, and they do know of people whose grey hair turns black again after age 90. I do not think there is a biochemical way to reverse the aging process, but in my 5000+ mg daily morphine base equivalent days, everyone stated it seemed to have shut off the process for 10 years of so and wondered if I was smoking cannabis for some reason. No, but have used tinctures of cannabis (improvised ones) to combat nausea.
If it is just slowing metabolism or some other effects, despite what the CDC in the US may say, narcotic use careers of around 100 years were first documented in the 1950s, and median life expectancy was lower then.