Wait a second. I thought they cast someone much older as Daenerys? Are they going to change the whole Daenerys/Rhaegar bit? If not...eh...not sure if I'll be watching. It was creepy enough in the book.
They aged her up to around 18, same as the actress. Pretty much everyone has been aged up, and they've changed the time line to accompany it; Game of Thrones happens 15 years after a rebellion that dethrones Daenerys' father, but in the series it'll be 20 years or so.
The character most ruined by being aged up is Robb Stark imo. In the first book he's about 15, in the series the actor looks 18-20. Robb goes through so much as a kid, and that sense of a kid being thrown into a deadly adult situation will be lost.