Age according to appearances

[Sagus]

Not sure if I agree on the ones in red. Shikieiki looks like a child in my opinion! To me, she looks 16 - 25...
hehe.... Please don't send me to hell!  :ohdear:
Mamizou looks about 30-39 to me...

Eh, I picture Shikieiki and Mamizou as looking older just because it feels more "right" to me, not because of anything in canon (although the "old hag" jokes regarding Mamizou certainly influenced how I see her).

[Alcoraiden]

Bwuh. This is purely from headcanon, but here are my answers, using the format I've seen in this thread:

Older Children - Age 7-9: Chen,
Preadolescence - Age 10-12: Rumia, Cirno, Daiyousei, Kisume, Shinmyoumaru, Wriggle, Mystia, Medicine
Young Teenager - Age 13-15: Flandre, Lily, Tewi, Nazrin, Benben, Yatsuhashi
Older Teenager - Age 16-19: Meiling, Remilia, Alice, Reimu, Prismrivers, Youmu, Aya, Sanae, Ichirin, Hina, Nitori, Momiji, Parsee, Seija, Maribel, Renko
Young Adult - Age 20-24: Patchouli, Nue, Letty, Marisa, Kaguya, Mokou, Reisen, Shou, Yamame, Satori, Koishi, Orin, Utsuho, Murasa, Seiga, Raiko,
Mid-Adult - Age 25-29: Yuuka, Mamizou, Yuyuko, Keine, Futo, Suwako, Komachi
Adult - Age 30-39: Shinki, Ran, Yukari, Shikieiki, Kanako, Byakuren, Miko, Tojiko
Middle-Aged - Age 40-50: Eirin
Older - Age 50+: Unzan

Left out Hatate, Akyu, Kasen, some Stage 1's, etc. because I either forgot them or they don't have assigned ages in my mind. So yeah, I think I don't like young Touhous all that much. ^^;

[Delfigamer]

How you dare doubt that Yukari is 19? This thread is useless. :<

[MaJO]

I believe that none of the girls believe they are over 29 and unmarried.

[Aya Reiko]

My own assessment...

No clue: Kisume
Other (??): Medicine, Unzan
Pre-Teen (10-12): All fairies, Rumia, Scarlet sisters, Chen, Suika, Tei, Suwako, Shinmyoumaru, Akyuu, Kosuzu
Early-Teen (13-15): Prismriver Sisters, Youmu, Wriggle, Mystia, Satori, Koishi, Nazrin, Kyouko, Futo, Reisen II
Late-Teen (16 or 17): Marisa, Reimu, Alice, Patchouli, Reisen, Nitori, Sanae, Tenshi, Yamame, Parsee, Rin, Utsuho, Kogasa, Nue, Hatate, Tojiko, Kokoro, Sekibanki, Kagerou, Tsukumo sisters, Seija, Kasen
Young Adult (18 or 19): Yuuka, Meiling, Sakuya, Letty, Kaguya, Mokou, Aya, Komachi, Aki Sisters, Hina, Ichirin, Minamitsu, Yoshika, Wakasagihime, Raiko
Adult (20-22): Yuyuko, Ran, Eiki, Yuugi, Shou, Byakuren, Miko, Watatsuki sisters
Twenty-something (22-29): Yukari, Keine, Eirin, Kanako, Iku, Seiga, Mamizou, Rinnosuke

all subject to change...