Sometimes this is logical, other times it seems like an attention grab. It is fairly common for certain communities on, for example, Livejournal to be overly sensitive to people's 'triggers' (often but not always relating to sexual assault)--any mention of violence may be censored.
Why having kids later is a really big deal. The average age of American women having their first child reached a record high of 26 years old in 2013, according to the Centers for Disease Control and Prevention's National Vital Statistics Report.
Then say that 20% of the 18-year-olds had a baby, 40% of the 19-year-olds, 50% of the 20-year-olds, and 30% of the 21-year-olds. Adding these up gives 140%, so the average woman in this hypothetical society has 1.4 children in her lifetime. Of course in real life women women are typically having children from ages 17 or 18 up to their 30's, and some have children even younger or older, so there are a lot more than four numbers to add together.