Hun:
He is a baby... a wild animal. He will be that way until you earn his trust.
There is no time line there. For Baby and I it took about a month for her to start coming to me, rather than fleeing from me. For Chief, bless his heart, he has wanted me from day one.
It is up to the bird and how much time it takes HIM to trust. The more you interact, the faster the process. But, you already know that huh.
I suggest when you go to get him, unless he REALLY wants to be alone, you persist he steps up. Otherwise, he will continue to flee to the back of the cage if he sees that makes you go away.
Man, if these birds werent smarter than us this would be a whole lot easier -sigh-
So, you have had that baby only a few weeks so dont get the slightest bit worked up. Get some spray millet and each time you get him to step up, give him some. He will then run to you when you open the cage.
Spary millet is UNDER-RATED. It is like crack to an addict, they'll do anything for it.