Baptism - http://www.biblicalfoundations.org/?p=85

This book just went on my wishlist :)

"First, the rite of baptism is designed for believers who have repented of their sin and have put their faith in God and in his Christ. Believer’s baptism is presupposed by both John’s baptism and the Matthean “Great Commission” passage."

"Second, baptism is an essential part of Christian discipleship. This is clear from the Matthean “Great Commission” passage, where disciple-making is said to consist of baptizing converts and of teaching them to obey the commands of Jesus (see also John 4:1)"

"Fourth, theologically, water baptism presupposes spiritual regenerationas a prevenient and primary work of God in and through the person of the Holy Spirit. This follows plainly from the Baptist’s announcement that the Messiah would baptize people in the Spirit. Thus repentance from sin and faith in Christ, accompanied by regeneration, are logically and chronologically prior to water baptism."

As a result of our new belief in Water Baptism - we come to ask ourselves - when is it appropriate to baptize someone?

I think the last paragraph there sums up the conclusion of the scriptures. Once a person is convicted of sin, decides to repent, has faith in the coming Kingdom Gospel, and experiences the very beginnings of the new creation that is the appropriate time.