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Those who baptize infants are bound by Canon Law to raise those children Catholic. A Catholic parent must
Can. 1125 1/โฆdo all in his or her power so that all offspring are baptized and brought up in the Catholic Church.
The Church prohibits secretly baptizing children* because it cannot be assured that the child will be brought up in the Catholic religion.
Can. 868 ยง1. For an infant to be baptized licitly [i.e., lawfully]โฆ2/ there must be a founded hope that the infant will be brought up in the Catholic religion; if such hope is altogether lacking, the baptism is to be delayed according to the prescripts of particular law after the parents have been advised about the reason.
*unless there is immediate danger of death
source: this answer to the question "Are there involuntary Catholics?"
Upvote:1
According to the Canon Law you need at least one of the parents to ask for the Baptism. So "legally" there is no need for the other to know or agree. Also, Baptism is a life-saving sacrament and it is denied in really few cases.
Regarding the age limit I think it depends on what your church defines as age from when the kid can be considered conscious of his decisions. In any case you should really ask for advice to your local priest or to the Bishop as well.