Nobody ever really plays their age in Hollywood, but there's no lie quite as big as when adults are passed off as teens on TV. It's understandable that producers would want to cast someone a little older if possible: They've probably got more acting and life experience to draw from, plus you don't have to worry about school or child labor laws if you hire someone over 18. And some actors actually do appear young enough for the illusion to work (Kristen Bell was 24 when Veronica Mars debuted, but damn if she didn't look like a convincing high schooler). But a lot of the time, you just get an adult awkwardly shoved into a kid's role, and that's when dramas become unintentional comedies. Some unrealistic TV teens fare better than others, but these are the worst of the worst. (All ages are pegged to the series' respective premiere dates.)

5. Charisma Carpenter, Buffy the Vampire Slayer Actual age: 26 Character's age: 16 As you'll see, many actors asked to play teens are a good decade beyond their actual teenage years. When Buffy the Vampire Slayer debuted on The WB in March 1997, the characters were all sophomores in high school. That means Cordelia Chase was probably 16, maybe even 15. Yet Charisma Carpenter was born in July 1970, meaning she was 26 when the show premiered and just a couple of months away from turning 27. She didn't look remotely like a high schooler, and as the show went on, she looked less and less like a teen and more like, well, a woman in her early 30s. When the spinoff Angel launched in October 1999, Carpenter went with the new show, and though the stories paid lip service to her character's age for a few episodes, producers eventually dropped all semblance of pretending she was 19 and let her dress and act her age. It works if you don't think about it too much.

4. Taylor Kitsch, Friday Night Lights Actual age: 25 Character's age: 15 Taylor Kitsch is in the kind of shape no human should be in. Born in April 1981, he was 25 years old when Friday Night Lights debuted in October 2006, even though his character, Tim Riggins, was just a sophomore at the time. (Sophomore characters are big in high school series. It gives the creators three years of stories before graduation, plus an easy out for the characters and a simple way to bring in new ones.) He never really looked 15 -- at the absolute best, he could have passed for 22 -- and his adulthood only became more pronounced as the show went on. By the time Tim left high school and tried to make life work at Riggins Rigs, Kitsch was treated like any other adult on the show.

3. Keiko Agena, Gilmore Girls Actual age: 26 Character's age: 15 Keiko Agena almost pulled a Kristen Bell. She looked young when Gilmore Girls launched in fall 2000, and she had the baby face and high energy of a teen. But she was already a solid ten years past her character Lane's age, and eight years older than co-star (and more believable teen) Alexis Bledel. Gilmore Girls liked its non-teens, too: Milo Ventimiglia was already in his 20s when he played the teenage Jess (who was much better than the wet sock that is Jared Padalecki, but that's a whole other thing).

2. Henry Winkler, Happy Days Actual age: 28 Character's age: 18 Henry Winkler's problem (such as it was) was that he never remotely passed for younger than his age. Born in October 1945, he was 28 when Happy Days hit the airwaves in January 1974, and he looked just about every day of it. There's nothing wrong with that, really, except that Fonzie was supposed to be a kind of teen or post-teen hood. By the end of the show, he was pushing 40. Guess that shark-jumping didn't pay off.

1. Gabrielle Carteris, Beverly Hills, 90210 Actual age: 29 Character's age: 15 Andrea Zuckerman wore big glasses and mom jeans, which didn't help her look young, but there was really nothing to be done. Gabrielle Carteris was born in January 1961, making her 29 playing 15 (!!) when Beverly Hills, 90210 debuted on Fox in October 1990. You read that right: She was about double the age of her character. Luke Perry was pretty egregiously old, too -- he was 24 when the show debuted but he looked older, because Luke Perry lives hard -- but Carteris was the worst. As the show aged, so did she, and it became increasingly ludicrous to watch a woman in her 30s act like she was emotionally invested in prom. She left the show after the fifth season to host a talk show, but since you aren't recording Gabrielle on your DVR, you know how that turned out.