Suspiciously Vague Age

Suspiciously Vague Age is a trope occurring in drawn or animated works where the story contains explicit sexual content clearly intended to depict those beneath the legal age of consent. For example, the story may depict high school students who build a relationship and later have sex. In this case, the characters are obviously intended to be somewhere between 15 and 18 years of age, which cannot be legally sold in many areas; the laws of the United States require everyone to be over 18 unless for tasteful artistic reasons, and in Japan it's 20.

In this case, everyone's age is conspicuously never mentioned. In some cases, this can lead to blatant lying where a character can't be as old as claimed when ages are given. The thing to remember about this trope is that either (A) the age given for the character is highly improbable (normal high school students being over 20) to impossible based on presented facts or (B) strangely never mentioned despite the obvious implications.

Very common in Dating Sims and Visual Novels, which do not have to employ actors who are over 18/20 and thus avoid the problem that way. See also Artistic Age.

No real life examples, please; tell the police, not us.

Examples of Suspiciously Vague Age include:

Anime and Manga

Hiroe from F³: Frantic, Frustrated & Female might -- might -- be a high-schooler, but we never hear anything solid about her age. Her older (maybe-)sister Mayaka appears to be college-aged, but all we can really be sure of is that she's old enough to drive.

Comic Books

Softpaw. Dear God, Softpaw. Some of the "18 or older" characters are first-graders.

Live Action TV

In Angel, Connor is originally stated to be sixteen after he returns from the hell dimension. However, when he needs to have sex with an older (mid-twenties) character, he's suddenly and specifically stated to be eighteen the episode before. Nice save, guys. Of course due to the bizarre circumstances of his upbringing none of them, including him, should know how old he really is.

Video Games

Dead or Alive, the localized versions refuses to give away the ages of the girls who are obviously minors: Kasumi, Ayane, Lei-Fang, Kokoro and etc. This because they're exploited to extreme cases of Ms. Fanservice byt wearing revealing to downright fetish clothing, due Values Dissonance in the west it wouldn't stick well for 17 and 16 old girls to be seen this way.
Utawarerumono avoids giving anyone's age, but little girl Aruru is estimated to be about the same age as busty Kamyu, putting their age at around 14 with Eruruw only slightly older.

Visual Novels

It's never stated outright, but both Da Capo and Da Capo II feature as their main character students who are in their last year of middle school, putting the main character at around fifteen and his love interests no more than one year older (Da Capo) or two years (Da Capo II) and both having heroines that are in their second year.
The heroines (and hero) of Fate/stay night initially appear to be of the improbable type, seeming to be of either normal or above average intelligence and yet first or second year students in what looks suspiciously like a high school despite being claimed to be "over 18" in the disclaimer. However, by taking Fate/Zero into account you'll realize that it's actually impossible for all the characters to be 20, (and even 18 requires some extremely implausible events). This is because Ilya was around 8 years old a decade ago in Fate/Zero, and is stated in Heaven's Feel to be older than Shirou. Since Rin is the same age as Shirou and Sakura is at least nine months younger than her, unless the two girls were put down several years they cannot possibly be over 18, and they certainly cannot be over 20 unless Shirou was put up several years. In addition, Sakura's birthday is given explicitly in Fate/Zero (although the year is not...), and is a month after the game, meaning that she would be a young first-year.
Yume Miru Kusuri lampshades it when the main character tells his obviously underage loli sister that she has to be over 20 because otherwise she couldn't appear naked in a game like this. Not that she gets any sexual scenes, but it highlights the tendency to do so.
- For that matter, any cast page for the game will have the characters listed as anywhere from 18-25 years old. Only the upper outlier, the clearly adult (and never sexually portrayed) Tsubaki, could possibly be accurate.
Sharin no Kuni has a notice saying all characters portrayed are at least 18 years of age. You can find this under the page with the helpful label of Blatant Lies.
The localization team for Family Project accidentally set off a shitstorm by promising the game would be completely uncensored, which was apparently a promise they couldn't keep when one of the heroines is really young even by the normal standards; Matsuri is probably about 13.
The main character in Kanon is a Second Year Protagonist with no indication that he's strangely older than he should be, putting the age of the cast between about 15 and 17. Makoto is probably younger, but doesn't really count for story reasons.
Nearly averted in Tsukihime. Arcueid is hundreds of years old and looks to be in her early 20s, Ciel really is older than she looks and Hisui and Kohaku have vague ages and could easily be at at least 20. Akiha and Shiki himself, however, have no excuse and are 16 and 17 respectively. Len falls into a related trope for Kagetsu Tohya.
Obliquely referenced in CROSS†CHANNEL; Taichi tries to press Miki about her age, but when trying to pin it down she gives very unnatural answers about how she cannot tell him her age. The obvious reason is that she's under 20.

Web Comics

In a Megatokyo filler strip, Dom mentions "tiny girls who are only legal because a writer stuck an 18 by the name."

Web Original

Very, very common in the "First Time" section on Literotica, and frequent in "Incest" as well.