Again, rightly or (for Baptists) wrongly, the church began baptizing infants at a fairly early date. It continued to be the normal practice until the emergence of the Baptists, albeit defended on a variety of theological bases.
I would like to know what you think an Early age is? In fact what is your reference for this? I know that Tertillian was opposed to infant baptism. And if I am not mistaken Origen gives one of the first references to it.
Again as others have recommended I would advise you to get Baptism in the Early Church by Hendrick F. Stander and Johannes P. Louw.
Here is a descent review of the book..
Here is the ARBCA sites review.
Baptism in the Early Church