Why would you be shocked? It's a medical fact that a lot changes biologically as we age, and it's also a medical fact that biology can greatly affect the mind. There's nothing magical about senescence.
That is not really clear to me. Biological changes can give us depression, irritability, mania, sluggishness, dementia and many other less-than-desirable mental states. What kind of change were you referring to that is fundamentally different from the things we know biology can do to a person?
