Hello and welcome to both of you.
In my experience the average age for a WBC, raised in a group of siblings or similarly aged babies to wean is 4 months. That being said a little sooner or later is fine as well.
It's hard to really assess a situation over the internet but I can definitely give you some ideas.
First, just to be clear, a weaned bird is one who eats enough food on his own (without handfeeding or assistance from a parent bird) to maintain his body weight day after day. Most birds will eat some formula if it is offered. So basically do not expect your baby to completely refuse to ever eat formula. If you offer it he will eat some, most likely.
As I sit here listening to my 3 1/2 month old WBC in the other room begging for food I can tell you that begging sounds and motions are an indication of not being weaned. So is acting desperate for food when you offer formula. Biting out of panic for food is a sign of not being weaned. Eating a full crop of formula is also a sign that he hasn't eaten enough food.
Birds who are weaned but are still interested in formula as a foodstuff act much more casual about handfeeding. The usually don't beg, they are never frantic or desperate to get to the formula or be fed and you should not have issues with them nipping at your hands in an attempt to get food.
If you baby is otherwise healthy I would suggest that you try two feedings a day about 10 hours apart. Let the bird wake up and eat anything that he wants in his cage or with you. Then in an hour or two offer formula, if he is not interested or only wants a little then let him eat what he wants and then be done with it. Feed a variety of foods in the cage all day. If he starts to beg frantically for food then offer more formula, if not then just offer some right before bed. See how it goes.
If he is not interested in the morning feeding for a few days then you can cut it out and just do the evening feeding.
It is really just an individual thing. If you have more questions please feel free to tag me.
