We are touching age this time, there're two factors when it comes to age in Gensokyo: physical and actual age.
Well, Physical is pretty obvious they're all in their late twenties of course. When talking about Actual age, things are going to get spicy. (Hotter than any
grandma one in Gensokyo.) I'll be using the Touhou wiki gensokyo timeline, Zun's statements and lastly my preference about Touhou to give out a fair judgment. Here is the timeline in Touhou wiki
Gensokyo Timeline - Touhou Wiki - Characters, games, locations, and more
The two stars of Touhou
Reimu: Unknown but couple of years older than Marisa considering 16 years are in-between EoSD and TH17. She maybe around 1992-1990, making her around 11-13 at the very start of Touhou project. Mentality an old teenager which is in 27-29. I wonder where the canon seal is?
Marisa: Couple of Years younger than Reimu. Thus, making her 24-26.
Starting off with EosD
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There aren't enough info so, please bear with me.
Rumia: there isn't a canon age for her but assuming the event of EosD she would be in 62-74 Youkai are old and she's in that range.
Daiyousei: same deal as Rumia in that same range. Another thing is that fairies are as old as the nuture.
Cirno: She was implied over 60 after the events of PoFV if my memories serve me correctly. Now would be 77-79 since PoFV came out 17 years ago. She is also part of the Nature. (Fairies are really confusing)
Meiling: if you want to go back to the ancient period, sure Qin dynasty. She might be 2400 years old, it ain't weird in Gensokyo. I have to take a guess in this one 110-160 sounds good?
Patchouli: Finally, some breath of fresh air. She's over 100 since she's born between 1885 and 1905. I'll call her 140 years old.
Sakuya: She might be riddled with Remilia power and there's also the Jack The Ripper theory, she'd alive in 1882. If you go with the timeline, she would probably be in her early 30s.
Remilia: Another breath of fresh air, she is 519 years old to the Gensokyo timeline.
Flandre: Yep, 5 years younger than Remilia.
Koakuma: No canon age, well, she is little devil not big devil. Might be a few years younger than Patchouli. I'll give her the 100 years pass.
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Next is PCB:
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Oh boy, another set of unknown canon ages,
Letty: Ok, if your going out with a Yuuki Onna, don't ask her, her age. Let's go back to Muromachi period: the 1336-1573. If we are using this as reference she is going to be 449-600-ish? Man, these're starting to be hard to guess.
Alice: Wait isn't she considered young for a youkai. For magicians passing the 100 threshold would be old. Since she's considered young, she might as well be in her 80s.
Chen: No canon ball for this neko cap'n. Cats would transformed to a bake-neko if they are simply too old. That CHEEENNNN might a few decade old sailor. Cap'n believe her to be around 22 years old.
Lily: Well, fairies again? Why am I judging each nature age? There's no canon flower blooming around this season. I suppose she'd be as old as the ice fairy if not younger. 65?
Prismriver Sisters: Oh my byakuren above there's no canon, centuries old should be logical? Lunasa-430, Merlin-460, Lyrica-445.
Youmu: I'll say she's in around 60 years old, hit or miss: her phantom half might have been existed longer??
Yuyuko: In her human era, she wasn't too old. Probably in early 20s/30s. She became a ghost 1000 years ago. This princess is over 1200. (Aya put her into your newspaper)
Ran: The 9- tails should be in her late 900s. The Unknown is the other way around.
Yukari: Older than the Gensokyo itself you're not *gap* (17), You're gapping over *gaps* (1200) like your ghost friend. Stop trying to interrupt me. There's is also one of my theory, that Yukari is created before the universe was and made the barrier between existence and non-existence. She could be millions of yeas old.
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U.F.O reached
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Whew, there's only one cloud that's missing.
Unzan: Why do you think the young kids called you grumpy? That's because you're missing out on canon. An old cloud sprit, well, if you can't find the current give it an original treatment: Cloud are seasons old but being a spirt makes you decades old, (20-40)
Narzin: A 1000 years old rat? That's not really old at all. Tell ya what scarvy, you're 1068.
Kogasa: Who left this umbrella over here for over 1000 years. Meanwhile, someone on heaven "shoot, I've left my 1074 years old cover."
Ichirin: Human truned to a
pokemon nyuudou trainer which is also over 1000 years? Bring me an older one. I.E 1057
Minamitsu: Cap'n there no cannonball left. What should we do? "Arrrr I became the captain of the Palequin ship between 825 C.E and 990." "I was human traveler like you once upon a time." (early 20s hit or miss) "But I took a whirlpool to the surface of the sea. Ie older than me mates possibly immortal." another over 1000 years, I said bring me an older one. You'll be scared, cap'n is in her late 1070s.
Shou: Ze tiger is over 1000 Starlingards. Most definitely older zhan Narzin. you're older zhan ze rat: 1080 Euro.
Byakuren: "Let the Touhou Jesus
Buddha show you the way of the youths." (Not mentioned over 1100 years old nun) Finally someone older than the 1139.
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Everyone's favourite IN
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My back is hurting but the canon fuse is missing in a couple of this area.
Wriggle: No more canon flies, shoot how old is a youkai fly? Make it 86, a tad bit older than the fairies.
Keine: 80?, over 1400? We don't know since she has forgotten about a 1434 years old canon scroll.
Mystia: The night sparrow is unknown but she is considered young as a youkai. 76 sounds pretty reasonable.
Tewi: If the White Rabbit of Inaba, she would be several centuries old, possibly older than Yukari or even Eirin. At least 1377 okay? Might be older than Yukari or Eirin (This is Gensokyo we're talking about.
Reisen: I'm certain she's over 40, partner. Perhaps older.
Eirin: Well, looks who decided to show up? 1300 year old pharmacist? Wroight, in Zun's words she is somewhere between 100,000,000's in age. Older than Moon god for sure.
Kaguya: 1300? Another Wroight. She is in the league with Eirin and Yukari's
Mokou: Born somewhere between 700C.E. Could be over 1300 years eh?
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PoFV joins in for smash.
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Some Breath of Air: the calm before the storm.
Komachi and Shiki: Hell is missing a canon letter from Heaven. Look, you can't even make sense out of this. They're both billions of billions ............................................................... billions, wait what number am I at? Better count from the beginning.
Aya: Settled in Gensokyo 1000 year ago. Over 1100 give or take.
Medicine: Immortal doll. I say she is a passing the 100 gap.
Yuuka: Over 60 but implied to be older. (What am I saying? This is Gensokyo)
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I'm too sleepy. The clock is also striking midnight. I'll cover MoF, SA, UFO, TD, DDC, LoLK, HSiFS, Spin offs characters, Manga characters and CD character. Feel free to correct if I'm wrong at the "cannon ball" age. Let's begin the torture tommorow. Good luck reading this and sequel. After all, I said this would be long.