It doesn't matter much that the suspect evidently is under 18 years old. Federal law permits the indictment of boys and girls for non-capital crimes. And since no victims died during the hijacking/piracy episode the death penalty would not be an option anyway following a conviction. Moreover, the circumstances surrounding any post-capture comments he may or may not have made shouldn't be a big deal, either. The feds won't need a confession here to be able to string together a very strong case. Captain Richard Phillips' testimony, alone, with the help of a little Navy videotape, would probably be enough to generate a conviction.
Can the suspect get a fair trial? It all depends upon what your definition of "fair" is. Federal judges no longer expect jurors to be blind to high-profile events—all they ask now is that potential jurors be able to put aside their pre-conceived notions about a defendant and judge him or her based upon the evidence at trial. In any event, I suspect that any trial here will not be the second coming of the OJ trial. The story of this crime has been played out in public for weeks—there will be no whodunit mystery that made the Simpson trial such a ratings winner.
The young man will be the first pirate to be prosecuted in America in centuries. That alone will make this an interesting story to follow. Justice Department lawyers right now are probably dusting off Jefferson-era precedent to see what sorts of defenses the suspect's public defenders will try to employ. And don't discount the possibility of a plea deal here—the teenager gets a sentence short of life in exchange for information about his fellow pirates (the ones who weren't killed). Sometimes a case is just overwhelmingly one-sided in favor of the government. This is one of those times.