I added a sibling as an additional card user on my BCE account. Of course, being that the sibling is only 15, I don't plan on giving the actual card to the said person until the person reaches the age of 18, sort of like a high school graduation +18th birthday present. Here's the deal: I haven't opened the envelope yet because I rather the person open it instead (would-you-give-an-open-present-to-someone type of thing) so the card remains inactivated till this day. Will American Express eventually cancel the card if it is to remain inactivated + unused for the next two years or so? Does this also mean that if inactivated + unusued, the card won't be reported?
I'd say activate the card; It may expire before they turn 18. If you want them to be able to open the envelope, order a replacement card a few weeks before they turn 18. They can open and activate that one.
I think if it is not activated eventually the AU account will never fully generate. Why don't you activate it, and order a replacement card on the 18th birthday? Once activated, it won't require any use at all.