Rite of Passage by Alexei Panshin

The year is 2205. One hundred and sixty-four years earlier, Earth had reached its catastrophic breaking point of Overpopulation (Panshin reckons that to be 8 billion humans). Accordingly, a lucky several thousand folks had crammed themselves into a hundred-and-some giant spaceships and simply Left. Earth didn't make it. The folks on the ships planted a few of themselves here and there as colonists on some of the crappy but habitable planets that they'd found, but the core of the Great Ship populations live and die and propagate on board said ships.

They are, understandably, hyperconscious of the evils of Overpopulation. The Solution: at age 14, every Ship child is jettisoned on a random (sometimes populated, sometimes not, but always entirely foreign and Darwinist) planet for a month. If the kid's alive when the ship swings back by in thirty days, then that Kid gets picked back up and is from that day forth an Adult. If not, good riddance.

I picked this up because it was on a list of Soviet Sci-Fi books that I've been looking for. Turns out Panshin was born and raised in Lansing, Michigan. One of his parents (I dunno which) was Russian. So, not quite Soviet--but this is a great book. It was published in 1968. And is told first-person from point of view of a 13-year-old girl. Which at first I thought would be annoying, but I was wrong--this book was the most fun I've had seeing the world through the eyes of a teenage girl since I read Random Acts of Senseless Violence.