The issue isn't really the right age, but whether he can respect boundaries - at 12 some kids can, others can't, it really depends on each one. Before you buy one, try it out with your phone or a friend's for a week and see if he can stick to rules like "no phone at dinner" or "maximum 1 hour a day"; if he can, maybe he's ready. If you do get him one, skip the really strict parental control apps (kids get around them and it becomes a constant fight) and focus more on having clear conversations about what he can and can't do - when there's trust, it works better than tight monitoring. What's your main worry: that he'll ignore the rules you agree on, or that he'll actually be glued to the screen even when you tell him to stop?