That's an odd coincidence, my headcanon for my Lavellan has her around 23 as well.
(Trevelyan is about 25/26, Adaar is 28 and Cadash is 35)
I headcanon Mayriya to be older, like 29 or something. 23 sounds good for a Tala though.
Edit: I'm on my ipad and can't get a good Solas picture up here, so instead, enjoy this made up party banter/dialogue for what I think would be a funny situation.
Ahem, enter scene of Lavellan, Solas, Cole and Cassandra walking by a large pile of dragon crap.
Lavellan: Creators have mercy! That smells awful!
Cassandra: See, everyone thinks they are so majestic, until they see this. *disgusted noise*
Cole: It was very relieved afterwards.
Solas: come here, vhenan, I know a spell.*casts spell on Lavellan's face to filter smell*
Lavellan: That's amazing, but I have a question.
Solas:Yes?
Lavellan: Why would one of the Creators take time out of their day to make sure the Inquisitor doesn't smell dragon dung?
Solas: Excuse me?
Lavellan: And this must mean you're Fen'Harel, the rest are locked up. Very sweet of the Dread Wolf to show such mercy I guess.
Solas: * panic look* I have no idea-why would you-
Lavellan: *bust out laughing* Wow, poor old Fen'Harel, can't even call a non-Dalish that name without them getting weird. It's just a joke, Solas.
Cole: Solas-
Solas: Quiet, Cole.!
*Solas greatly disapproves*