Hi Xavier ,
It depends on what you call "tame" . If you want birds that are hand tame and will sit on you or be extremely friendly you have to handle them as soon as their eyes are open . Touch , stroke , hold them frequently ( a lot ) , talk to them so they get accustomed to you and they will have little fear and will let you handle them or sit on you when older.
I call "tame" is when they come when I whistle and get within a few feet of me , show little fear and I can tell they enjoy being around me .... but they wont actually tolerate me picking them up unless I corner them in the coop and they have no choice

. They'le flock to me ...but a bit wary .
It depends how much time you want to put in with them , each bird is different too . Some are just more trusting and friendlier than others .
Even older birds ( and ferals ) will get pretty tame if you are around them a lot and treat them right .
Trust is the thing , you have to earn their trust . They like human companionship . Remember though once you get them really tame you have taken on a responsibilty to look after them as they lose that self preservation instinct .
hambone