Notice how every year people are more and more suffering? The older man, the more unhappy becomes. The longer his life lasts, the more he suffers.
In fact, the relationship between the number of years and suffering is only that a person is gaining experience. Somewhere he made a mistake, incorrectly calculated his strength, did not show wisdom to something, at some point he missed a chance. The suffering of man is rather accumulated experience than the number of trouble. Please note that a child has fewer suffering because he knew little and survived. The adult has happened more unpleasant moments in life, so it suffers deeper and thoroughly.
The elder man suffers more because of his memories that it happened to him. The longer life, the more suffering, and their source is bad memories. People love to dive into their own memories of missed opportunities and committed mistakes.
You can not suffer because of what was once in the past and today it does not matter! Why remember the past and spend nerves on it? A person makes himself unhappy only because he enjoys suffering, deprivation, mistakes that occurred in his life. But why pull the whole cargo of trouble if you can live what matters today? The more often the person remembers the unpleasant past, the more suffering.