Lyric discussion by haruki 

Cover art for Power Of Not Knowing lyrics by Kings of Convenience

I think you're a little off. I think the song as a whole describes a love affair between an older man and a younger girl. I see the first verse as entirely describing the young girl in question. The speaker is talking to a young girl trying to act older than she is–she's embarrassed by how young she seems in comparison to her older peers and is trying to be like them.

In the second stanza, the (presumably) older speaker is trying to impress upon her the gift that is youth. Obviously he feels he's lost some of the redeeming "power" of being unsure and young, perhaps the power of opportunity and being able to more easily steer one's life. He tries to hang on to that in his own life, and searches for someone young to come along.

Then, in the final stanza he expresses regret for perhaps somehow tarnishing this young girl over the course of their relationship. He worries that his presence has stolen her youthful energy and glow through his actions in their relationship and that she can never reclaim it.

My Interpretation