The people who say “attack them with siege in early castle” are talking utter nonsense.
Britons are the BEST civ in the game at stopping siege pushes in castle age because their xbows make siege useless.
The problem with your idea of “you need a build order” assumes the existence of generic units that can beat Britons as any civ.
No, half of the civs in the game, if not more have no answer to Britons.
You just die if they play properly.
But the rest of the civs have very easy wins.
Koreans 1 range skirms into war wagons is a free win.
Eagle civs get a super easy time of it.
But none of these are generic options.