We know more about the age of human trafficking victims today than we know about their ages in the 9th Century BC.
In the U.S., the average age for entering the sex trade is 13.
But the Bible does not tell us the age of the temple slaves. Those ancient authors mentioned hardly any details about the Asherah temples.
My guess is that their readers knew all about the temples, so the writers felt no need to load them up with everyday data.