She was 21 since the end of FF13. Since time does not flow in Valhalla she is still 21. In reality she been on the world for over a thousand years (By comparsion Fang and Vanille will had been at least 1500 years assuming they are still alive). However she had literally seen all of time repeatedly so mentally she is like a million years old.
Lightning Returns will surpass 13-2 and become accepted by haters! Official Noctis Lucis Caelum of the XV board.
She's over a thousand and still gets carded at bars. Most women would be jealous of that.
I'm sure most women would be fine when they realized she had to spend most of those years alone in this place. http://www.ff-xiii.net/images/media/4e69bf3a_Final-Fantasy-XIII-2-Valhalla-3.jpg
What do you mean alone? She had Caius, a homicidal maniac who tries to kill her whenever he sees her in his quest to destroy the universe, and Etro, the perpetually incompetent deity who created the entire mess, for company!
Currently going "squa squa squa!" To the Devil May Cry franchise: http://25.media.tumblr.com/tumblr_ls0e5g1oWn1qjkv09o1_500.gif... at least for now.