the revealed ages coming from the Pokémon Tera leak:

8 years old - Bonnie, Hapu

9 years old - Poppy

10 years old - Wally (he was 12 in the beta), Lucas/Dawn, Barry, Maylene, Iris

11 years old - Red (Gen 1), Blue (Gen 1), Ello/Selene, Hau, Lille, Acerola

12 years old - Ethan, Brandan/May, Lucas/Dawn, Lyra, Nate/Rosa, Clemont, Lana

13 years old - Gladion, Ilima

14 years old - Red (Gen 2), Blue (Gen 2). Roxanne, Hilbert/Hilda, Cheren, Bianca, Cilan, Chili, Criss, Benga, Korrina, Mallow, Kieran

15 years old - Rei/Akari, Roark, Elesa

16 years old - Winona, Candice, Calem/Serena (they were 14 in the beta)

17 years old - Caitlyn (Sinnoh BF), Mina, Nessa

18 years old - Gardenia, Skyla, Shauntal, Viola, Kiawe

19 years old - Aaron, Morgan, Plumeria

20 years old - N, Caitlyn (Unova E4), Valerie, Diantha

21 years old - Burgh, Guzma, Kahili

22 years old - Brawly, Grant

24 years old - Volkner, Dahlia

25 years old - Jessie, James, Flannery, Steven, Darach, Siebold, Dendra

26 years old - Ryuki

27 years old - Cyrus, Cynthia, Grimsley, Marshal

30 years old - Maximo, Marlon

32 years old - Fantina, Kukui

33 years old - Malva

34 years old - Shelly, Wallace, Olivia

35 years old - Professor Birch, Lenora, Wikstrom

37 years old - Norman, Crasher Wake

40 years old - Drasna

41 years old - Mohn

42 years old - Argenta, Lusamine

43 years old - Looker, Wicke

44 years old - Brycen

45 years old - Wulfric

50 years old - Professor Oak, Pryce, Nanu, Mustard

51 years old - Byron

53 years old - Faba, Ryme and Tyme

55 years old - Clay

56 years old - Bertha

57 years old - Alder

65 years old - Ramos

67 years old - Wattson

69 years old - Drayden

70 years old - Professor Rowan

71 years old - Charon

77 years old - Hala

88 years old - Opal

99 years old - Calaba

3,000 years old - AZ