Well, what are your boundaries on "consider"? I remember entertaining the possibility of God's existence at a pretty early age -- somewhere between two and four, but infantile amnesia's eaten the specifics -- but always as a hypothetical, a playing-pretend game. It took me quite a while to realize that my peers weren't consciously participating in a pleasant fantasy; as late as age eight or so I remember making decisions that could only have been predicated on the opposite assumption.

For context, I was raised in a pretty obviously Christian cultural milieu -- picture books of Bible stories, a sense that it was normal to go to church on Sundays even if you and your parents didn't -- but most of my very early authority figures didn't make a conspicuous show of belief. "Secular" might be the word, but only implicitly so.