I was traveling during the 2023 US Open, so let this thread slide. Here it is all in one big info dump in advance of updating for 2024 Australian Open.
N.B. Ages as of August/September 2023
US Open 2023, Men's Singles 3rd Round
18: Mensik [turned 18 on Friday 1 September - during round 3, so made it to round 3 at 17]
20: Alcaraz, Shelton
21: Draper, Stricker
22: Arnaldi, Sinner, Baez, Hijikata
24: De Minaur, Davidovich Fokina
25: Rublev, Tiafoe, Fritz, Gojo
26: Zverev, Mmoh, Zhang, Paul
27: Medvedev, Jarry, Bonzi
28: Norrie, Rinderknech, Djere
29: Karatsev [turned 30 on Monday 4 September - during round 4]
30: Vesely
32: Dimitrov
33: Evans
35: Mannarino
36: Djokovic
38: Wawrinka
By Age Bracket:
15-19: 1
20-24: 10
25-29: 15
30-34: 3
35-39: 3
Men's Singles 4th Round
20: Alcaraz, Shelton
21: Draper, Stricker
22: Arnaldi, Sinner, Hijikata
24: De Minaur
25: Rublev, Tiafoe, Fritz, Gojo
26: Zverev, Paul
27: Medvedev
36: Djokovic
By Age Bracket:
15-19: 0
20-24: 8
25-29: 7
30-34: 0
35-39: 1
Men's Singles Quarter-Finals
20: Alcaraz, Shelton
25: Rublev, Tiafoe, Fritz
26: Zverev
27: Medvedev
36: Djokovic
By Age Bracket:
15-19: 0
20-24: 2
25-29: 5
30-34: 0
35-39: 1
Men's Singles Semi-Finals
20-24: Alcaraz, Shelton
27: Medvedev
36: Djokovic
By Age Bracket:
20-24: 2
25-29: 1
35-39: 1
Men's Singles Final
27: Medvedev
36: Djokovic
By Age Bracket:
25-29: 1
35-39: 1