The following is a list of the youngest male tennis players and champions at the U.S. Open. I've been playing tennis for over four decades now, and the game definitely favors younger players. As I age, I cannot get to shots I used to get to and when competing against younger opponents I have to use guile to win.
The same is true for professional tennis players. The vast majority of Grand Slam singles championships are won by players under 30 years of age. Some players do win Grand Slam events after age 30, but that is not the norm.
Youngest tennis players and champions at the U.S. Open (Men)
Youngest men's singles champion at the U.S. Open
The youngest man to win a U.S. Open singles title is Pete Sampras . Pete was 19 years and 28 days old when he won the U.S. Open in 1990. Sampras defeated 20-year-old Andre Agassi by a score of 6-4, 6-3, 6-2 in the final to win the title.
Youngest men's doubles champion at U.S. Open
The youngest man to win a doubles title is Vincent Richards, who was 15 years, 4 months and 26 days old when he won the doubles title in 1918.
The youngest man to win a doubles title in the Open Era, after 1968 when professionals could compete at the Open, is Lleyton Hewitt. Hewitt was 19 years, 6 months and 13 days old when he won in 2000.
Youngest man to win a mixed doubles championship at the U.S. Open
Vincent Richards is also the youngest man to win a mixed doubles championship at the U.S. Open. Richards won the mixed doubles title in 1919 when he was 16 years and 3 months old. Richards is the youngest player, male or female, to ever win a mixed doubles championship at the U.S. Open.
Youngest man to compete at the U.S. Open
The youngest man to ever compete at the U.S. Open is Tommy Ho, who was 15 years, 2 months and 14 days old when he played a first round match against Johan Kriek in 1988. Kriek won the match in straight sets. Despite playing at the Open at such a young age, Ho's career never amounted to much in large part due to injuries.
Youngest man to win a match at the U.S. Open
The youngest male player to ever win a match at the Open is Vincent Richards again. Richards was 15 years, 5 months and 8 days old when he won a second-round match vs Frank T. Anderson in 1918. Richards automatically advanced to the second round in 1918 when his opening-round opponent withdrew.
The youngest man to win a match at the U.S. Open since the Open Era began is Michael Chang. Chang was just 15 years, 6 months and 10 days old when he defeated Paul McNamee in the first round of the 1987 Open.
Michael Chang made a U.S Open final (1996) in his career but never won the tournament. He is, however, the youngest male player to ever win a Grand Slam singles event, as he won the French Open in 1989 at the age of 17 years and 110 days. That was Michael Chang's only Grand Slam title in his career.