Game of Thrones' third-season renewal came as no surprise, though it did prompt the first wave of "how are they going to do this?" questions, since the third "Song of Ice and Fire" book is pretty darn long. The most pressing question for fans isn't how the show will condense and approach the text, though: It's how they'll account for the kids on the show growing up.
GoT has a lot of young actors. Maisie Williams, who plays Arya, is currently 15; Sophie Turner, who plays Sansa, is 16; Jack Gleeson, who plays Joffrey, is around 19; and Isaac Hempstead Wright, who plans Bran, is 12. Without spoiling anything, let's at least acknowledge the possibility that not all of these characters live to see the end of the series — but that still leaves some key players who are aging much faster than their characters.
Let's assume the series splits the third book's contents in half, as the producers have suggested, and also assume that HBO will renew the show for a fourth and fifth season. (Safe bets!) Producer D.B. Weiss has stated that the show runs on a twelve-month production cycle, and that it's "really all we can do to do 10 of them in a year," which means the show won't be doubling up by shooting two seasons at once. Thus, by the time the show starts getting into A Feast of Crows territory, actress Maisie Williams will be 17. Five years will have elapsed in actual time since the show started, but only about a year and change will have transpired in Westeros time. The entire written series so far takes place over roughly three years, but the show will take six years just to catch up to where the books stand now.
The adaptation has accounted for some of the age gaps already, casting both Daenerys and Robb Stark as older on the show than they are in the books: Ambiguous aging from mid- to late-twenties is of course far less noticeable than going from, oh, 14 to 19. The show has cast young-looking actors in the kid roles, too — particularly Gleeson, who was convincingly playing 12-year-olds at 17. But this season already he looks substantially older than he did in the first, and that affects how Joffrey operates on the show. Petulant, prodigy boy-king is markedly different than petulant, scary grown-up king.
So what's a show to do? Recast periodically? Ignore normal growth and hope no one cares? Something more like the latter is more appropriate here, not just because the cast is good, but also because strict time markers are not fundamental to the series. Part of the underlying sense of doom in Thrones comes from the warpedness of time. Winter's coming, but not in a predictable, four-seasons way, and it will last such a terrifyingly long time, we're not even sure how to measure or articulate that span. The books tend to use relative time — "three days later" but not "that Thursday" — which gives the TV show even more flexibility. As long as the plot points happen in order, the exact time doesn't seem to be essential.