I see you are in the Netherlands. I am unsure how these transactions work in Europe, but in the US, typically a prospective buyer will put down a deposit (part of the money) for the bird to hold it and pays the rest at the time they pick the fully weaned baby up. It is very important the breeder gives the bird as much time as it needs to wean naturally, which can be shorter or longer depending on the individual. A baby bird weaned before it is ready can have behavioral problems for life. It is also a high likelihood an inexperienced new owner could harm or kill the baby trying to hand feed it themselves. It takes an experienced breeder to do this properly. Baby parrots are very sensitive. It makes NO difference in the ability for the parrot to bond to it's new owner if the baby comes home fully weaned from the breeder.
I can't help but wonder if there may not be a communication error here. Are you certain the breeder is not suggesting they hope to sell the bird by next month (i.e. have someone commit to buy it, give them a deposit etc...) but will not be sending it home for another 6 weeks/until it is weaned or do they actually want to send it home with you as soon as you buy it, still needing hand feedings? You need to clarify this with them. NO reputable breeder sends unweaned babies home with people who have no idea how to hand feed. That may even be illegal in Europe, as you have tighter laws regulating the sales of parrots. Otherwise, keep looking for a more reputable breeder who would not put a baby bird in danger by sending it off unweaned to an inexperienced new owner.