I was peering over the table intently, taking in every 'spiritual morsel', at the age of 4. I recall believing it was the 'truth' at that point - though I certainly had nothing with which to make comparison. I was not 'born in' either - Mom had just begun to study at that point. I practically memorized all the WT artwork, since I could not read, and I often answered questions in the study.
I am sure it is a matter of personality. But mine drew me hard and fast to the teachings. I recall 'knowing' that it was wrong to attend another church, that Jehovah was God's name, and that only by being a good JW could one actually gain life forever.
I believe what is said about children when they are likened to a blank slate or a dry sponge. Very limited exposure to something that begins to fill in the voids, will have a major impact.
In my case - though my mother was basically an inactive, non-attender, beginning right after baptism for her [when I was 5] . When we moved to California at the age of 8, I daydreamed that we were moving to a place that likely lacked a Kingdom Hall, and imagined myself finding a way to get one built there. Though it was discussed at home very little - I self-restricted myself from anything 'worldly' at school - celebrations, flag salute, school activities. One of my favorite pastimes as a child, was to gather up all the old Watchtower and Awake magazines, hole punch them, and make my own 'bound volumes'. I recall at the age of maybe 9, telling my mother that I would not eat the meat she had just prepared for me, because it had blood running out on the plate. By the time I was 14, though I had likely attended fewer than 30 meetings in my life, I had become so eager to 'serve Jehovah', so hungry for it, that I rode my bicycle 9 miles to the Kingdom Hall one Sunday, alone, down back roads, then back home again.
All that - and my exposure following my mother's baptism was just old WT literature laying around the house and an occasional visit from Witnesses to try and activate Mom, and maybe those 20 or 30 meetings. And Mom's occasional 'reminders' about Jehovah in conversation.
Years later, one of the elders who studied with my Mom, said he recalls that I was the one he was sure would become the Witness in the family. He could see it in my eyes when we talked about the 'truth' when I was 5 or 6.
That early exposure made me into a 'little Witness' even though I got virtually no encouragement in that direction for years following. My case may not be typical - but something to think about.
Jeff