Sari looks older because she's a battle hardened veteran.
In most RPGS/Fantasy stories, the warrior queens and princesses and soldiers always look older due to the strain of training and fighting. Some examples could be:
We could say Titania from Fire Emblem: Path of Radiance
Eirika from Fire Emblem Sacred Stones
Lyndis is also an example from Fire Emblem. She is 15 and 16 in Eliwood's part.
Melvina from Growlanser: Heritage of War is another example.
So is Captain Sherris.
Lyndis and Eirika are two of my favorite warrior princesses. Melvina is my 3rd.
I think it's the training and fighting that ages people. You don't have much time to enjoy youth when you train to kill.
Besides, the best example is.. Laya XD She's 1000 years old and doesn't even look it!