Here I've added the winners' names for each event. I also found a couple errors in the WPA list, so I have corrected those.
WPA World 9-Ball Championship
15-20 -- 1 (Wu)
21-25 -- 2 (Archer, Hohmann)
26-30 -- 11 (Strickland, Strickland, Chao, Ortmann, Souquet, Archer, Takahashi, Immonen, Pagulayan, Ko, Ouschan)
31-35 -- 4 (Chao, Alcano, Peach, Hohmann)
36-40 -- 3 ( Akagariyama, Appleton, Feijen)
41-45 -- 3 (Okumura, Reyes, Strickland)
46-50 -- 1 (Bustamante)
51-55 -- 1 (Varner)
Total -- 26
US Open 9-Ball Championship
15-20 -- 0
21-25 -- 4 (Sigel, Strickland, Deuel, Van Boening)
26-30 -- 13 (Hopkins, Roberts*, Sigel, Hopkins, Howard, Strickland, Kennedy, Morris, Owen, Pagulayan, Van Boening, Van Boening, Cheng)
31-35 -- 13 (Mizerak, Sigel, Howard, Strickland, Pierce, Archer, Souquet, Jones, Schmidt, Appleton, Appleton, Van Boening, Van Boening)
36-40 -- 6 (Reid, Reyes, Strickland, Strickland, Immonen, Immonen)
41-45 -- 2 (Varner, Varner)
46-50 -- 1 (Hall)
51-55 -- 2 (Lebron, Hall)
Total -- 41
Distribution for the two events combined
15-20 -- 1 (1%)
21-25 -- 6 (9%)
26-30 -- 24 (36%)
31-35 -- 17 (25%)
36-40 -- 9 (13%)
41-45 -- 5 (7%)
46-50 -- 2 (3%)
51-55 -- 3 (4%)
Total -- 67
Note -- The age used here is year of event minus year of birth. For any players whose birthday occurred between the date of the event and the end of that calendar year, their actual age last birthday on the date of the event was 1 year less than I used.
*The age used for Louie Roberts (29 in 1979) is an estimate, as I have not yet found a reliable source for his year of birth.