Starhawk, thanks for clarifying the Icaran view of adulthood. It's interesting that the advanced educational practices in the story result in a social situation reminiscent of "primitive" Napoleonic Europe, when "children" labored alongside adults in the fields, shops, and armed forces, and often married in their early teens. The lack of automation in Icaran society (explained in an earlier post, as I recall) would tend to provide ample opportunities for inexperienced workers.
However, recent scientific studies suggest that the Icarans may be employing more than just advanced education here. Apparently the part of the human brain affecting judgment, self-control, planning, and organization doesn't fully develop until age 20 or after. If so, it would seem even highly trained teenagers would be at a disadvantage in unfamiliar situations, compared to their older peers.
On the other hand, the Icarans can probably pick and choose the best young recruits (even for the Working Navy), and teenagers tend to live up to what's expected of them. Under a strict merit system, the Icarans can promote the mature teens and defer promotion of the late bloomers. I found it interesting that the youngest crewman mentioned in the story is a female; even in the future, perhaps females still mature earlier than males?
As for jailbait, if the Icarans only recruit "adults" then the "problem" doesn't exist (presumably the age of majority is also the age of consent). However, the view that all the older "adults" would prefer their own company to that of the younger "adults" seems a bit naive--the novel "Lolita" isn't entirely a work of fiction. As an Icaran ship's captain, I'd tend to keep the cabin boy away from the chaplain, "adult" or not.
PBS's look at the neuroscience of adolescence:
http://www.pbs.org/wgbh/pages/frontl...ows/teenbrain/