In 1860 Baltimore Benjamin is born with the physical appearance of a 70-year-old man already capable of speech. His father Roger invites neighborhood boys to play with him and orders him to play with children's toys but Benjamin obeys only to please his father. At five Benjamin is sent to kindergarten but is quickly withdrawn after he repeatedly falls asleep during child activities.

At the age of 18 Benjamin enrolls in Yale College but is sent home by officials who think he is a 50-year-old lunatic. When Benjamin turns 20 the Button family realizes that he is aging backwards.

In 1910 Benjamin now looking like a 20-year-old turns over control of his company to his son Roscoe and enrolls at Harvard University. His first year there is a great success: he dominates in football and takes revenge against Yale for having rejected him years before. However during his junior and senior years he is only 16 years old too weak to play football and barely able to cope with the academic work.