touhou characters by apparent age in art vs. reported age

1. Yagokoro Eirin (1500+) 1. Futatsuiwa Mamizou (?) 3. Yakumo Yukari (1200+) 4. Hijiri Byakuren (1100+) 5. Yasaka Kanako (2000+) 6. Nagae Iku (?) 7. Letty Whiterock (?) 8. Kazami Yuuka (60+/old) 9. Horikawa Raiko (100+ (as taiko drum)) 10. Junko (?) 11. Kamishirasawa Keine (adult) 12. Reiuji Utsuho (Okuu) (older than underworld) 13. Matara Okina (knew Kasen) 14. Kumoi Ichirin (1000+) 14. Yakumo Ran (800+) 16. Patchouli Knowledge (~100) 17. Hong Meiling (?) 18. Wakasagihime (?) 18. Imaizumi Kagerou (?) 20. Kishin Sagume (goddess) 20. Fujiwara no Mokou (1300+/immortal) 22. Onozuka Komachi (60+) 23. Miyako Yoshika (dead?) 23. Hata no Kokoro (~1300) 25. Hoshiguma Yuugi (old friend of Suika) 26. Sakata Nemuno (?) 26. Usami Sumireko (15-16) 26. Ringo (?) 29. Saigyouji Yuyuko (1000+/died as teen) 30. Shameimaru Aya (1000+) 31. Kaku Seiga (1400+) 32. Soga no Tojiko (1400+/dead) 33. Toyosatomimi no Miko (1444) 33. Kochiya Sanae (younger than Suwako) 36. Houraisan Kaguya (1300+/immortal) 37. Aki Minoriko (younger than Shizuha) 37. Izayoi Sakuya (probably 100+) 37. Kagiyama Hina (goddess) 37. Ibaraki Kasen (500+?) 41. Alice Margatroid (?/Younger than Shinki?) 41. Reisen Udongein Inaba (40+) 41. Koakuma (?) 44. Mononobe no Futo (1400+) 44. Toramaru Shou (1000+) 44. Hakurei Reimu (60-?) 44. Kaenbyou Rin (Orin) (older than underworld) 48. Inubashiri Momiji (49+/"especially long-lived") 49. Sekibanki (?) 49. Lunasa Prismriver (same as other prismrivers) 49. Doremy Sweet (?) 49. Seiran (?) 49. Hecatia Lapislazuli (?) 55. Aki Shizuha (older than Minoriko) 55. Wriggle Nightbug (?) 57. Kurodani Yamame (?) 57. Tsukumo Yatsuhashi (?) 57. Komeiji Satori (probably older than the separation of Hell) 57. Shiki Eiki, Yamaxanadu (?/Immortal) 62. Murasa Minamitsu (?/knew Byakuren before her sealing) 62. Hinanawi Tenshi (?/Celestial) 62. Mizuhashi Parsee (?) 62. Teireida Mai (?) 66. Konpaku Youmu (60-) 66. Kirisame Marisa (about reimu's age) 66. Kijin Seija (?) 66. Komeiji Koishi (youner than Satori) 66. Tsukumo Benben (older than Yatsuhashi) 71. Kawashiro Nitori (?) 71. Nazrin (1000+) 71. Houjuu Nue (800+) 74. Kasodani Kyouko (?) 74. Nishida Satono (?) 76. Remilia Scarlet (~500) 76. Moriya Suwako (2300+) 76. Tatara Kogasa (?) 76. Komano Aunn (as statue, probably as old as Hakurei Shrine) 80. Yatadera Narumi (?) 81. Kisume (probably before 1984) 81. Daiyousei (?) 81. Merlin Prismriver (same as other prismrivers) 81. Eternity Larva (?) 81. Flandre Scarlet (~495) 81. Inaba Tewi (1300+) 81. Ibuki Suika (several hundred+) 81. Rumia (young?) 89. Chen (?) 89. Clownpiece (?) 89. Lyrica Prismriver (same as other prismrivers) 92. Cirno (60+?) 93. Medicine Melancholy (nonliving, very young (by youkai standards)) 93. Mystia Lorelei (young) 95. Sukuna Shinmyoumaru (?)
1. Yakumo Ran (800+) 2. Yagokoro Eirin (1500+) 2. Kumoi Ichirin (1000+) 4. Izayoi Sakuya (probably 100+) 4. Kazami Yuuka (60+/old) 6. Kishin Sagume (goddess) 7. Patchouli Knowledge (~100) 8. Fujiwara no Mokou (1300+/immortal) 9. Saigyouji Yuyuko (1000+/died as teen) 9. Mystia Lorelei (young) 9. Tsukumo Yatsuhashi (?) 12. Junko (?) 12. Yasaka Kanako (2000+) 14. Inubashiri Momiji (49+/"especially long-lived") 15. Horikawa Raiko (100+ (as taiko drum)) 15. Futatsuiwa Mamizou (?) 17. Tsukumo Benben (older than Yatsuhashi) 17. Aki Shizuha (older than Minoriko) 17. Reisen Udongein Inaba(40+) 20. Letty Whiterock (?) 21. Hijiri Byakuren (1100+) 22. Kaku Seiga (1400+) 22. Miyako Yoshika (dead?) 24. Lunasa Prismriver (?) 25. Nazrin (1000+) 25. Hoshiguma Yuugi (old friend of Suika) 27. Sekibanki (?) 27. Yakumo Yukari (1200+) 27. Kisume (probably before 1984) 27. Daiyousei (?) 27. Wriggle Nightbug (?) 32. Konpaku Youmu (60-) 32. Shiki Eiki, Yamaxanadu(?/Immortal) 32. Mizuhashi Parsee (?) 32. Kagiyama Hina (goddess) 32. Wakasagihime (?) 32. Hong Meiling (?) 32. Tatara Kogasa (?/100+(as umbrella)) 32. Kurodani Yamame (?) 32. Kamishirasawa Keine (adult human) 41. Mononobe no Futo (1400+) 42. Koakuma (?) 43. Kochiya Sanae (younger than Suwako) 43. Komeiji Koishi (younger than Satori) 43. Chen (?) 43. Reiuji Utsuho (Okuu)(older than separation of Hell) 43. Shameimaru Aya (1000+) 48. Soga no Tojiko (1400+/dead) 48. Houjuu Nue (800+) 50. Toramaru Shou (1000+) 50. Komeiji Satori (probably older than the separation of Hell) 52. Houraisan Kaguya (1300+/immortal) 52. Seiran (?) 52. Lily White (?) 52. Ibuki Suika (several hundred+) 52. Himekaidou Hatate (?) 52. Remilia Scarlet (~500) 52. Toyosatomimi no Miko(1444) 52. Murasa Minamitsu (?/knew Byakuren before her sealing) 52. Lyrica Prismriver (?) 52. Flandre Scarlet (~495) 52. Hecatia Lapislazuli (?) 52. Rumia (probably young) 64. Hinanawi Tenshi (?/Celestial) 64. Ringo (?) 64. Imaizumi Kagerou (?) 67. Nagae Iku (?/Celestial) 68. Kijin Seija (?) 68. Sukuna Shinmyoumaru (?) 68. Cirno (60+) 68. Kirisame Marisa (about reimu's age) 72. Clownpiece (?) 72. Kaenbyou Rin (Orin) (older than the separation of Hell) 74. Inaba Tewi (1300+) 75. Moriya Suwako (2300+) 75. Hakurei Reimu (60-) 77. Alice Margatroid (?/Younger than Shinki?) 77. Aki Minoriko (?) 79. Onozuka Komachi (60+) 80. Medicine Melancholy (nonliving, very young (by youkai standards)) 80. Doremy Sweet (?) 80. Merlin Prismriver (?) 80. Kasodani Kyouko (?) 80. Kawashiro Nitori (?)
why is the series full of "looks young but is actually million years old" characters
In most cases it's because they're actually gods (and so can presumably appear however they like) or youkai (where the scale is just very different from that of humans, ~100 is more or less a child and only 1000+ begins to be considered old) and then in there are discrepancies based on species, how the creator (who is not known for being good at art) originally drew them (and stuck), and the anime factor.
but lumag how can be so old if touhou was only invent in recent?
well actually Touhou is just the name of the place they live in since it was constructed as a safe haven for youkai that mostly already existed (i.e. they moved to Touhou from our world circa 1990-2000), some are older than the creation of Touhou