accident at the age of 20
c) a middle aged person commits suicide shortly after retiring
(comment as if you would take the form of a letter to the dead person, expressing your reactions to his/her death
Have you noticed the most interesting elements of these three deaths? In all three cases, the common element is the potential realized or unrealized by the person's death.
What might you say to an infant who doesn't even know what he or she is missing? Would you focus on an afterlife for this infant? Would you console the infant by saying that even though there was no potential realized, the infant has missed the pain of living?
The young person who has "promise," who dies at 20, would be completely aware that the potential was unrealized. What can you offer such a person? Perhaps you could say that he or she was lucky to have experienced a childhood and adolescence filled with promise. Perhaps you could say it is better that he or she lived at all, that this was a death preferable to a death in infancy.
The adult who commits suicide after retirement I would speculate had suffered from clinical depression. But there are other possible reasons. Perhaps the person had a degenerative or fatal disease and wanted to have control over his or her destiny. Perhaps the person had realized all of his or her potential, and was simply tired of life. Perhaps the person had found retirement to be a disappointment. If I were writing to a suicide, I would have many questions!