Dean died at twenty-seven and Sam ten months later at not quite twenty-four; Dean goes to the crossroads for Sam, like Dad did for Dean, because Dean can't live with only memories of Sam.

Dean died at twenty-nine and Alastair tells him at irregular intervals thereafter that Sam's dead: a week in, Dean laughs in his face, because he knows damn well that Lilith (tore Sam apart) ran the moment Sam remembered he was holding the knife that could get him the revenge Dean knows Sam would want; eighteen years in, Dean laughs in his face, because he knows damn well that Sam's (a reverse silhouette on the Fremonts' wall) long since gotten out, away from anything that could want him dead, excepting the kids he's sure Sam wanted, probably teenagers who're as much of a headache as Sammy ever was; thirty years in, Dean doesn't laugh, because Sam's fifty-five (if Sam's alive), older than Dad ever got—Winchesters are matches, flare bright and hot and briefly, do the job and they're done—the whole point of all this is Sam alive, and if he no longer is...

Dean died at thirty-one and Sam at twenty-seven; they're together when they bring Lucifer down and together when they tell the reaper to get lost and together as they speed along every two-lane road in America, muscle and metal and memory and a tale that's sometimes true.