Did anyone else expect the love/body dilemmas toward the end to play out completely differently? I was sure the book was building to Ian asking Wanderer to live in his body, after which Kyle would ask Sunny to enter him. As it was, it was almost like the possibility didn't occur to Meyer.
I thought it was fairly obvious why that wasn't a viable option: the human soul may be suppressed by the Soul. If that wasn't an issue to contend with, I thought a threesome (foursome) would have worked.
From what I recall of Ian and Kyle's mindsets at that point, they'd happily have accepted being "suppressed" rather than let the people they cared about die or be exiled, which were the only alternatives they had until the final chapter.
Why did Wanda have to lie about her age? Melanie is a human - her mental maturity and physical maturity are roughly the same, so issues with age difference between her and Jared make sense. Wanda's body is sixteen, but why does that matter? As an alien, she's significantly older mentally. Age of consent laws are based on mental maturity - the age a person can reasonably be assumed to understand the implications of having sex. Why does it matter how old her body is when Wanda the soul has lived several lifetimes?
Wanda didn't actually have to lie about her age. She was just remembering how it happened with Melanie and Jared: even though it was the Apocalypse, Jared didn't feel comfortable doing anything with Mel because she was underage. Knowing Ian is ever the Gentleman, and could get hang up in these details, she lied to avoid him fretting over her age. Basically, she just wanted to have sex.