The aging process is fascinating because it doesn't disturb me, because this is what it is supposed to be like. But I'll tell you what does - it's the lack of strength - you can't hold up suitcases and do it yourself. Loss of physical strength.
The aging process seems to strike first at the mechanism which warns that we have been talking too much and the listener is growing restless. The signal isn't perfect at any age - drink, for instance, throws it right out of kilter - but it is almost non-existent in old people.
A is for Alibi, my first book, was published in 1982. As it happened the next couple of books took place in June and August of that year. Without meaning to I painted myself into a corner. The other issue was the aging process. I did not want my main character to age one year for every book so I slowed the whole process down. This way I could get through all 26 letters of the alphabet without making her 109 years old in 2015. I might end the series in either 1990 or on New Years Eve 1989.
I came to what I think of as the critical problem: the aging process of a piece of music. I noticed in the '70s that pieces I wrote would sound great the first time I listened to them and then on repeated hearings they sounded older and older until what seemed exciting and vibrant on first listening became stale.