Fear is a response to a real threat whereas anxiety is a response to a perceived threat. When you differentiate them in this way, I think it becomes clear that, as we age, the amount of fear we experience decreases and the amount of anxiety we experience increases. Why? I think because we can become immune to, or numb to, threats that are real as we experience more of them. This is why exposure therapies work for phobias like a fear of heights. But the opposite happens with imaginary threats; the more we think about them, the worse they get. The ultimate cause of anxiety is our own death, but death is not something we can experience first-hand, which means it can never be a real threat to us. Even to the last minute, death will always be an imaginary threat. So, as we get closer and closer to death, our anxiety keeps increasing, although our fears decrease.