A Question for Fellow "Believer's Baptism" Folks: Discerning the Proper Age

A couple weeks ago my brother Garrett emailed me this quote from Tertullian:

Baptism is not rashly to be administered... And so, according to the circumstances and disposition, and even age, of each individual, the delay of baptism is preferable; principally, however, in the case of little children... More caution will be exercised in worldly matters: so that one who is not trusted with earthly substance is trusted with divine!

Garrett noted: "Interesting thought: until we are willing to trust a person with earthly responsibilities and possessions, maybe we shouldn't trust them with heavenly things."

This observation led to an ongoing conversation about what age is appropriate for baptism. Often these discussions turn on what seems ultimately to be an arbitrary choice: when are you an "adult"? When are you "able" to pledge allegiance to Christ for life, aware of what you are doing and saying, and mean it?

The problem isn't only about infant versus believer's baptism, as this quote from James McClendon demonstrates. Here is part of McClendon's critique:

Meanwhile, the churches of the baptist vision have widely responded to the same societal pressures that generated the Constantinian practice, making of the great death-and-resurrection remembering sign a pale cultural symbol, administered to every young child who displays religious feeling (often sincere), and who seeks (as would be normal in childhood's latency period) to emulate admired older persons and to rival other children of the church. So in many baptist churches baptism is still responsive, yet it often fails to be responsible.

As a lifelong member of one of those small-b baptist churches (namely, churches of Christ), this is 100% on the mark. Teenagers who are baptized are at least in murky territory -- but more and more, I am seeing children in elementary school baptized, children whose voices of confession clearly lack puberty's advance. Given the commitment to believer's baptism, is this really any different -- morally, theologically, or psychologically -- from infant baptism?

Here was my simple answer to Garrett's query about the proper age for baptism, either in America or elsewhere: the age at which a culture deems an adolescent to have been initiated or made the transition into adulthood. Depending on time and place, this will be signified by the expectation or possibility of marriage, and/or of having children, and/or of living alone, and/or of owning property, and/or of concluding basic universalized education, and/or of working for one's own or one's family's sustenance, and so on.

Is this view controversial or problematic? Is the rush prior to this stage of adolescent/adulthood transition primarily about fear of damnation? Is it about wanting to "grasp hold of" or to affirm any expression of faith before it withers away? Is it because Americans in particular view the church as a kind of extended family-friendly institution, so the more professing children, the better?

Whatever be the case, I welcome responses and thoughts. And let me reiterate: the assumption of this post is believer's baptism. We have discussed paedobaptism in its own right elsewhere. My question is about, for, and to Christians committed to baptism as the event of a person's conscious confession of Jesus as Messiah and Lord, initiation into his body, washing of burial with him, and rising into the resurrection life of his Holy Spirit. Within that commitment, how ought we to go about discerning the proper age for such an event?