That's MY generation!
Few of them were ever raised in Christianity. Their parents were probably just unchurched (Christians rejecting "organized religion") but as a result, their kids were not raised in the church and rarely raised as Christians.
As I look at my parents generation (Baby boomers), the issue there is usually the church (not Jesus). Many of them claim to be at least very loosely "spiritual Christians" (and they are certainly theists who believe in heaven, prayer, etc.) but, because of their rejection of the church, often, all this is off the radar of their kids. "Christianity is always one generation away from extinction."
Additional comments.....
The Baby Boomers (born 1945-1964) and whatever you call the next generation (born 1965 - 1980), I think many of them were raised as Christians and "from infancy" were taught at least SOMETHING about Christianity. I think they TEND to not only be theists but also regard Jesus at least in very high regard. They tend to have some respect for Scripture (maybe a lot) and often see their religion as a source of comfort and direction. The problem is: a LOT of them have issues with institutional Christianity, with denominations. IMO, this not infrequently is a result of their parents likely being "mixed" (coming from different denominations), because of the century's old denominational wars, but probably mostly because they don't see the institutional church as very helpful in terms of comfort and direction. Their "issue" is not with God (or even Christ), but with churches..... their "religion" is spiritual (and largely based in prayer and God as a sort of fairy godmother who watches over them). And it tends to be negative toward theology and teachings since such seems to run against the raging relativism of our day and seems to just drag them down into denominational infighting. IMO, "winning over" these people has little to do with their relationship to God but to the church.
My generation (born 1980-2000) have largely been raised as godless, pretty much as Agnostics. Many of my generation have never been to church and never been taught anything about Christianity. Their view of Christianity is benign - neither good or bad. It (and the churches it produced) are seen as something very significant from our PAST as a society. It produced a lot of good art and music, and obviously helped a lot of people in very trying times (both pluses), but it's just seen as irrelevant. If they are open at all, they want a church that supplies their wants: Great music (yes, it can have very Christian lyrics), sermons that will help them be richer and happier, studies that will help their marriages and their raising of the kids - in other words, to live better. Jesus.... God..... Scripture...... well, they are VAGUE things but helpful toward the goal of being a more successful, happier person. The "worship hour" needs to be entertaining, uplifting and practical/helpful; the focus very much on what it does for self in the here and now. But a LOT of my generation has been to those "churches" and found them kinda weird.... still others got involved for a few months, maybe even a few years.... and found them to be not really helpful at all in making them successful in the here and now, a failed commodity not worth the time and money, and so dropped out. My generation is littered with LOTS of "mega church" drop outs. But even more who simply never engaged at all with Christianity... it seems to them something important to their grandparents (and that's nice) but they aren't sure why.
Just my experience.....
- Josiah