I don't think you guys got off track. It is not about age, but about understanding the gospel message (theology, but the gospel). I was saved when I was ten. I questioned for a time if it was genuine (I didn't understand sin as I do now, I didn't understand redemption as I do now) but I realized that I was saved with the faith of a child....but that faith included understanding the gospel of Jesus Christ.
And I don't think people intentionally tell unsaved people they are saved to get numbers. Pastors genuinely want people to be saved regardless of theological differences. But sometimes I do think we get careless when offering assurances of salvation. My personal fear would be carelessly giving false assurance to someone and that person standing before Jesus as He says "I never knew you." There are people who think that they are saved but are not, I don't doubt that at all.
We can never truly know if someone is saved. But we can do our best to help people understand the gospel and discern to the best of our abilities if they confess true faith. It is not preventing anyone from entering the kingdom, in fact, it is the opposite. And it is being responsible.