Mustang
I grew up as a jw but at the same time because my mom didn't convert right away I went to roman catholic schools. Where I lived the sacrament of confirmation was done in grade 7, and while I myself didn't go through it, I was taught all the prep material along with the class. Its believed that it came into being when local priests were given the duties to baptize and then when the bishop visited the church, he'd perform a second anointing of those baptized as a confirmation.
You're right on about the spiritual meaning given to it. Its a confirmation of the person's baptism and what that initiation entailed. The person is confirming their wish to be part of the church of God and to be followers of Christ. Its about affirming the christian identity when they're old enough to understand the basic tenets of the faith. The sacrament is said to give one a closer tie to God/Jesus, the Church, a fuller bestowing of the gifts of the Holy Spirit, as well as one being better able to defend the faith, or at least receiving more strength and determination to live it. The Bishop normally conducts the sacrament and it has a person being sprinkled with holy chrism (holy oil). They were encouraged to take on a confirmation name for themselves to emphasize the point about taking on this other christian identity.
Not sure what else I can tell you. It was a long time ago. Everyone was urged to wear white if I remember correctly. At least I remember seeing alot of pictures with my male schoolmates in silky white suits and every body was comparing who was more queer looking...for once I wasn't in the running.