I'm not sure how to answer...
I went to church, VBS, camp, etc, when I was younger, and accepted Christ and was baptized in July of 1993 (I was 9). But throughout much of junior high and high school, I didn't have a clue - I completely gave up on God, didn't care...I didn't consider myself a Christian anymore at that point.
My senior year, God really started working in my life, through some amazing people, and I began to seek Him again, and I rededicated my life to Christ on July 5, 2001...
So I think I'd have to go with less than a year...cause even though I knew about it, I definitely feel as if I've really just learned about God's grace for the first time, and it's so awesome