Right after the first scene, the wedding, it says 11 years 9 months later...and the girls say they are 11 years 9 months old. They would have to be born on the night of the wedding for this to be true and their mom didn't look pregnant.
I noticed this too. They would have had to be 12 or 13, maybe 14 for it to be realistic. But if the twins were conceived on the night of the wedding, it would've been over 12 years later.
heres what happened
nine months after the wedding the twins are born
in most movies the subtitle that say "3 years later" or whatever don't mean exactly 3 years later
so 11 years 9 months later mean that the girls are at least 11 years old but not 12
This is what really happened..
It is a slip-up.
They tell other people that they will be 12 in October. If they go to camp during the summer, as most people do, that means that they are (roughly) 11 years and 9 months old. The person who submitted this slip-up is correct in saying that they would have to be born on (or extremely close to) the day of the wedding.
Well, the twins' mother could have been two months pregnant at the time of the wedding. Then their age would be about accurate. Because then seven months later, possibly six, they would be born, and then they WOULD be 11 years and nine months old. So, I hope you understand what I just said, because I sure didn't. oh well.
It is true that they will be twelve in October, but in a interview, the directors said that they had put in the "11 years and 9 months later" in for a purely comedic effect.