That's a very good analysis. This is the part that interests me most:

bagelwoman:

it appears from the studies that the capacity for decision making may decline during puberty and immediately thereafter, as they show that risk-taking peaks during adolescence. So it may be that an 11 year old who hasn't hit puberty has better decision-making skills that 13 year old who has.

Second, I don't think it's convincing that after that point, a child may be interested in sex or act in ways that evince interest, willingness, or complicitness. The whole point is that the child cannot think through those actions or fully make decisions about that interest.

I wonder whether these two arguments converge on a paradox, i.e., that at puberty you become more likely to be interested in sex (see e.g. <link>) and -- at the same time and for related reasons -- less capable of making rational decisions about it. So you have a tradeoff between the emotional and rational components of sexual maturity, which doesn't resolve until years later (if ever).