I think it comes down to a question of what you believe the church is doing when you baptize. You might think that you are merely telling the church that the person has professed faith in Christ. So anyone who says he's a Christian and wants to be baptized, you baptize: the upper-middle-class tidy-life couple, the town drunk, or a 4-year-old kid.If you want to make the argument that conversion and baptism are linked in Scripture, I'd agree. Wholeheartedly. In fact, it's precisely because I agree so strongly that I think it's generally unwise to baptize young children. Frankly, I believe there's a far greater problem in contemporary American Christianity because we regularly baptize unconverted young children, than there is because we unreasonably withhold baptism from the genuinely converted.
On the other hand, if you think baptism is a declaration of allegiance to Christ, affirmed by the church, and linked to church membership with all its privileges and obligations, then you're going to think it's pretty important for there to be some sort of examination of the credibility of the person's profession.
If you go the latter route, you're going to have to ask yourself (in light of Scripture) what constitutes a credible profession of faith, and at what point a child is ready to bear the burden of congregational rule and accountability to church discipline. It's very difficult to discern the credibility of that profession in the life of a young person, particularly one inclined to fear of man and people-pleasing, while the child is under the primary care and authority of his or her parents. For that reason, I'd do all I can to avoid baptizing a pre-teen, and the more I'm seeing in pastoral ministry, the higher that age is getting in my mind.
In other words, I'm arguing that we have a foundational problem in our understanding of conversion. We really need to get that problem sorted out before we get too upset over people "delaying" baptism—or before we give any more kids the false impression that they're eternally secure.
Finally, I don't know of a better combination of theological clarity and practical application on the matter of baptism than what you'll find in this book—one of the most helpful things I've read in the past five years.