Good Morning Mr. Death

What is it that we never think of when we're young, but is constantly on our mind when we get old?
A 16-year-old wannabe thug meets Mr. Death, who takes him on a tour of his world. He shows him the souls he has collected and the souls he will collect.
If Wendell Tate can solve Mr. Death's riddle, his soul will not be the next one collected.