While everyone will experience age-related skin thinning to one degree or another, some people are more prone to it than others. Genetics is a major player in skin thinness. So, if your parents had noticeably thin skin, chances are you will, too.
Another possible contributor to the thinning of skin is the long-term use of medications like corticosteroids. If you're on such a medication and you're worried about thin skin, ask your doctor if what you're taking is the best option for your condition. Even if it is, there are ways to improve care of your skin.
The following page addresses a potential treatment for thin skin.