Some quick searching reveals that this seems to be changing due to online discourse:

How old were the minors trafficked in the Epstein-case

The victims in the Jeffrey Epstein case were minors — overwhelmingly teenage girls — with reported ages spanning from early adolescence into the late teens; official federal court materials cite victims “as young as 14,” while civil complaints and news reports have claimed victims as young as 11, 13 and 16 in specific allegations

4. How language, sealed deals and settlements shaped public understanding of victims’ ages

Legal maneuvers — notably the secret 2008 non‑prosecution agreement and sealed filings — obscured the full record for years and limited public insight into precise victim counts and ages, contributing to variations in public reporting and the proliferation of civil claims when more documents were later unsealed [10]. Media guidance and public sensitivity also shaped descriptions: newsrooms corrected and cautioned against euphemisms like “underage women,” urging the terms “minors,” “girls” or “children” to reflect victims under 18 [12]. Settlements and redactions in civil litigation further complicate a single, authoritative age list [10].

My guess is that adolescent teenagers are sometimes referred to as “young men” or “young women”, and are generally distinct from prepubescent children. Given the early and ongoing obfuscation of the evidence, perhaps it’s an over-correction by the media towards generalized language. Teenage sexuality also exists, although when an adult is involved it’s legally referred to as statutory rape. Generally, the especially heinous “child rape” or “child sexual abuse” is reserved for pre-adolescents.

Here’s an interesting article detailing NPR’s editorial process after it used the controversial term “underage women”:

By 5 a.m. the next morning, Sprunt's introduction had been reworked again, this time adding the inappropriate description of the victims. Marrapodi said the staff was trying to ensure that victims' voices are present whenever appropriate

Marrapodi said several people were collaborating on the script and so he's not assigning responsibility to a single person.

As NPR is a more a left-leaning, independently open, and sympathetic news organization, so I found it particularly interesting that they made this mistake. Someone on their review staff put the term back in during the editorial process and it makes me wonder, why would they?