It's a game. Maybe they just changed the law in AWAM version of the country the live in, or Dylan was thought to be older because he is with Sophia. In the end, it doesn't matter at all. As long as the game remains coherent, everything is fine.
Even more, AWAM is intended to be a porn game. So it is almost mandatory that not everything that happen in this game also would make sense in the real world. Sometimes I get really confused about how much L&P ramblings about a realistic game have messed up the expectations here. No matter which of the stories you look at, all of them will have to go down this path sooner or later. If this game were realistic (for the real world), nothing fun would happen at all in this game. L&P would have to virtually omit all events except maybe the events between Sophia and Liam.