It was Walt's 52nd birthday at the Denny's in episode 1 during the flash forward, and he turned 51 during the normal timetable of the season. So we have plot armor for a good while after he gets the big fucking gun. DEA is going to be on his ass soon, or at least Hank and friends... I wonder if Skylar will break down and off herself or something during this time. Walt's daughter is probably going to be the lynchpin of the story I'd imagine... some homer simpson "do it for her" kind of shit