Actually, the photographs are spaced ten years apart, not sixteen.
1912 to 1922.
The young, homeless (but no less dapper) wanderer shown in the first survived the sinking of the Titanic and swam to the shores of West Egg. There he built a life and a large, empty house, in an effort to win the heart of the wealthy, upper class woman he’d fallen in love with a decade earlier and had been separated from against his will.
He shed his earlier identity, and changed his name to reflect his new station. Jack was now known as Jay Gatsby, the eccentric millionaire who threw parties every night in the hopes that one day his love would show up and spin with him as they had long ago in the dance hall of the lower decks.