Aging the characters a bit shouldn't be too horrible (although I did have a bit of a pout at reading that they're going to age them). I just hope they don't go too far in the aging process and make Cersei look like she's maybe 30 and Joff look like he's in his 20's (for example). Also, they can always "Dawson" cast the characters if they have an inappropriate scene when they're much too young.
However, I have to agree with the person who asked them not to give in to the temptation to make Dany into a sizzling hot 20 something year old character.
As to Sansa's flowering and age, if they upped it to...say...15, it's still realistic for her not to have flowered as some flower as late as 16, especially if they've lived active lives.