As an archaeaologist, I could tell you someone's age below around 18 with a moderate degree of accuracy, from bones and teeth, because of the relatively well understood and regular pattern of tooth eruption and bone epiphyseal fusion - although there can be differences of some months between individuals, and some factors allow greater precision than others. Above that it becomes more inaccurate, and the changes we look at are based more on environmental and social factors, like diet or level of physical activity, because then it's mostly based on wear and tear - worn teeth (much less with a modern soft diet as opposed to the rough diet of ancient people) and arthritic changes on the faces of the joints (more likely in people undertaking hard physical labour)
Of course, I'm more used to dealing with bones I can pick up and handle and examine closely. I'm not up to date on how much of this evidence is clearly visible on X-rays etc.