At the start of the movie when John Conor is talking he says that he had met Arnold when he was 13, but in fact he was 10 (looking back at Terminator 2)

because if you look at set years for the first 2 movies they are only 10 years apart. Even though he may look 13, he's still 10. Even if he was 13 (and I'm wrong) it would'nt mach up to his age in Terminator 3 of 19. This is because there is 9 years between 1994 and 2003. If he was 13, Terminator 3 would be set in the year 2000, 6 years after the 2nd movie.