I don't think they mean that, I think they'r ejust complaining about the odds of the age of new slaves being children vs teen or adult?
SexiestManAlive, It's basically an even distribution right now, should be equal chances of child, teen, and adult, if all 3 are enabled. Might just be that due to bad luck all the slaves worth buying/capturing/keeping have tended towards child? There's the Maturing elixir which raises their age so you can correct that, but rather than the biased pool that is your own house, look at the set after you beat groups of enemies, should see roughly similar distribution.