As far as I'm aware, according to manga we know that Ymir's curse lasts for 13 years because once 13 years passes the vessel (person) is done serving its purpose.
Judging by Annie's appearence in her crystal for the last few chapters I can say with confidence that she didn't age physically at all. She appears to be the same height and her hair hasn't grown any longer, just untied. Of course, she hasn't had any intake of food of drink and had little to no sunlight exposure either, so it would make sense that she didn't age. And unlike Willy's sister she isn't conscious inside her crystal either.
If Annie comes out of her crystal then, how many years would she have left?
If the clock of Ymir's curse still ticks even while a shifter is crystalized, and assuming she comes out in present time immediately, Annie would only have about 2 years left.
However, if the curse of Ymir calculates time spent based on how much the holder has aged, then Annie could easily still have 6 years left in her life once she comes out.
I personally hope that the 6-year scenerio is true, since I do see the possibility of Annie waking and joining the new nation of Eldia, and if that happens I'd like it if she lived longer.