Youmu is probably older than she looks -- it's hinted that half-ghosts age slowly -- but she's certainly less than a century old.
As for the others, yes. Yuyuko died over 1000 years ago; Yukari is at least 1200, probably much older; Tewi is considered to be the oldest of the youkai beasts in Gensokyo, at somewhere over 1300 years old; Eirin was already old 1400 years ago when Kaguya was born and was probably involved in the Moon Capital's founding eons ago; and Suwako was an ancient established god when she and Kanako fought 2300 years ago. "Old ladies" doesn't even begin to describe it.
N2O said: Not sure about Youmu, but everyone here is old, right...?
No force in the universe can get her to leave Yuyuko's side? And any force nevertheless inclined to do so has an intimate meeting with Misters Point and Edge?