IMHO.. what we called 'tame' is actually their trust. If they trust you, they become tame. Although the degree of 'tame' varied.
I bought a pair of adult bantam chicken. And they were not tame (at least to me) back then. And what makes it worse, When we just brought them home and my dad wanted to put the Roo in the coop, the roo escaped

And we must chased him around to catch him. This makes him traumatic, I guess. It's quite difficult to approach him after that.
I fed them very little food, but very often. I fed them probably 6x /day because I want the food container to be empty when I visit their coop, and I want them to know that my visit = more food. And after I add more food, I sit in there for a while ( I have a small bench in the coop). I want them to see that I'm not a threat. I also do the cleaning or anything in the coop without even look at him. I ignored him completely. I put a radio nearby so they can hear human voice.
After 1 week, I started bringing treats. I gave them meal worm.. but they didn't want to eat from my hands so I throw the meal worm a little bit farther. I gave them cucumber too. After they tasted the treats for several days, I changed the way I give treat. If they want the treat, now they must come and eat from my hand. The Hen came and started eating from my hand although the roo didn't.
Another 2 weeks passed, and now whenever the hen is eating from my hand, I use the back of my hand to rub her chest area. I didn't grab her. Only a gentle rub. And now I have a tame hen although she didn't let me grab her. The Roo obviously observed all of this. He saw that the hen was OK. I'm not a threat at all. So, now he let me get close to him and use the back of my hand to touch him a little bit. He still refused to eat from my hand though.
After I had them for 2.5 months.. the roo started to trust me a little bit more. Now, he is willing to eat from my hand. But only for treat.. not the regular food. But this is a progress.. of course. Another 2 weeks.. and the Roo is tamed now

I can just walk to him and pick him up.
Basically, let them set how fast they can start trusting you. Don't rush things. I know it is frustrating if you want to pet your chicken and they flight. But if you take it slowly and patient.. they will come around eventually.