When I was first exposed to Christianity in the American South, I was exposed to the Missionary Baptist faith. That is, Baptists who are Calvinists but believe in evangelizing (i.e., missions work). This is opposed to the Primitive Baptists who are so strongly-convicted about their Calvinism, they do no missions work at all. These two groups split off from each other a few centuries ago. Of course, being Baptist, they taught that baptism by immersion was vital, but not as a salvific act. It was an important proclamation of faith. Being baptized meant that you were publicly announcing that you have already become a Christian, and that baptism symbolically shows you have already died with and been reborn into new life through Christ. The act of baptism does nothing, but is an outward sign of inward grace already imparted by God to the new believer. Of course, to believe and make this proclamation one must be of this magic "age of reason" in order to understand the decision you're making. As I got older I ventured into other traditions. Without fail, as long as the congregation of the church was Evangelical Protestant, this was their perspective on baptism, regardless to what denomination the church sign said out front. It seems to be the default understanding for all Evangelical Protestants.
This is completely at odds with the Orthodox Faith. Baptism is not an outward symbol of a work already done in the heart. Rather, baptism is the carrying out of that work, the reception of that grace itself, not a symbol of it. We are baptized for the remission of our sins, not because we understand our sins or because we understand God's grace. How presumptuous it is to say we understand God in such a way! We aren't baptized for knowledge's sake. We're baptized for Christ's sake, for the remission of our sins by uniting ourselves to Christ. For many converts, we do willfully choose to be baptized as adults because we weren't baptized into the Church as infants. However, for those blessed with pious Orthodox parents, they are brought into the church for baptism, for the remission of sins. To be united to Christ, even as babes, that they may grow up in the Church.
This is no different than being born Jewish. Jewish boys never got the choice about being presented in the temple for circumcision (and, personally, this is something I'd want a little more say in than being dunked in some water!), yet they were brought and admitted among the People of God through the act itself. Even to this day, male converts to the Jewish faith must be circumcised (even as adults). Just as circumcision initiated a person into the covenant people, so now does Holy Baptism initiate us into our Life in Christ, uniting us to His death and resurrection. It's not about understanding a concept, it's about knowing a Person. It's about the remission of sins. It's about life everlasting.