One of the interesting results from psychology is that emotions are a complicated feedback loop from stimulus, around through the body, back to the feeling, but

One of the interesting results from psychology is that emotions are a complicated feedback loop from stimulus, around through the body, back to the feeling, but critically involving bodily response, not just states of the brain. I've personally experienced "feeling anxious" simply because my heart was beating too quickly for purely physiological reasons. (I've had some heart troubles.) Once I addressed those reasons, the anxiety faded with it. This is a handwave in the direction of this research and ideas, not an explanation of it; consult the web if you're interested in more. I propose something that neither the article nor anyone else is in the comments so far, which is that we age, our bodies simply get less physical about the emotions. It makes it easier to be more level if your body is literally being more level, and the aforementioned feedback loop is literally weaker. Everything else gets weaker in old age, why not the physiological strength of emotions, too?