I wouldnt need a baby anyway because conures can sometimes live to be very old but would it be harder to get a 10 month old conure rehomed because of allergies to trust you then a baby?
I truly think it is better to go for the bird that is most needy rather than being rather selfish and going for the one that is the youngest. When a bird bonds with you any training can be done well. It just takes time and understanding of their needs.