As someone who grew up in Orange County, the son of religiously and politically conservative parents, I have had the chance to observe many of my peers and the different paths of their lives, from childhood to adulthood.
I grew up in the evangelical Christian culture that is so prominent in Orange County, as evidenced by the numerous evangelical mega-churches: Saddleback, Mariners, Rock Harbor, The Crystal Cathedral, and The First Evangelical Free Church of Fullerton (aka EV Free). I attended EV Free regularly from ages 7-18, and most of my childhood friends went there too.
Of particular interest to me are my friends who remained religiously and politically conservative vs. my friends who left the church, or at least the evangelical church they grew up in. The numbers seem to be about 50/50.
I must confess from the outset that I am in the camp who left the church, and the religious/political ideology it represents. Interestingly enough, many of my friends today are people like me, who grew up in the church but, as adults, left it for ideological reasons.
I will offer some observations, first regarding those who stayed in the church. The first primary factor that determines whether or not someone will stay in the church is getting married young, ages 20-25. Many of my friends who stayed in the church married young, thus cementing their place in church culture. As a consequence of marrying young, many of these folks had children young, further cementing their place in the church. The kids go to sunday school, and the parents go to some sort of "adult fellowship" group, a subgroup of the larger church congregation body.
I believe the contemporary evangelical church, particularly EV Free, is essentially a family affair. There is a "singles group" but it is relatively small and quite depressing.
So, young marriage and family are the primary factors among my friends who remained in the church. This is interesting to me because these peoples' choice to stay in the church often has less to do with belief, and more to do with marriage and family circumstances.
By contrast, then, many of those who left the church are those who remained single past age 25. Another factor is attainment of advanced degrees like M.A, Ph.D, or MFA (with the exception of any advanced degree from BIOLA). Other factors include: a propensity for creative expression, reading, pop music, intellectual exploration, foreign travel (non-missions related), cigarettes, alcohol, and casual sex.
Granted, this is not a scientific study. It is simply some insights gleaned from my observations and experiences.