Some people contemplate their lives and realize they are dissatisfied. they realize that missed opportunities have passed, and that they have not accomplished what they wished. according to the theory of psychoanalyst erik erikson, these individuals experience

Hey there!

Erik Erikson developed and proposed 8 psychosocial stages of life. These, in order, are trust vs. mistrust, autonomy vs. shame, initiative vs. guilt, industry vs. inferiority, ego identity vs. role confusion, intimacy vs. isolation, generativity vs. stagnation, and ego integrity vs. despair. 

It sounds like the last one, ego integrity vs. despair, is described in your problem. The last stage begins around maturity, or 65, and goes on until death. At this stage, people are often retiring or are retired, and start pondering the things they didn't do with their lives. This leads to regret about not doing certain things that they once hoped to do, or maybe didn't even realize they wanted to do at the time. They think that it's too late now, and start feeling dissatisfied with their life, as your question describes. 

Hope this helped you out! :-)