Timeline and ages

So in season 5 Tom says the war has gone on for 3 years and in the first season he mentions that Hal is 16 years old. When Pope has kidnapped Hal and Tom finds a group of people he asks if they'd seen a man in his mid 20's lol. So Hal is supposed to only be 19 by now, yet he's mid twenties? Matt was 8 when the war started and he's 13 by the end. Honestly, how do they get things like this wrong?