The film contains a classic "Freaky Friday" Flip premise, but with a twist. After an experiment by kid genius Willie Donovan goes awry, his divorced grandparents Cat and Gene are somehow turned into teenagers. Cat is the spitting image of granddaughter Sydney, while Gene reverts to his attractive former form.
Everything is great in teenage-land until it is revealed that the effects of the backwards aging are unexpectedly dangerous. It is up to Willie to get his grandparents back to their normal ages and for his estranged grandparents to find their ways back to each other.
Seventeen Again contains examples of:
- Accidental Murder: What could've happened to Willie if the grandparents died!
- Actor Allusion: Tahj Mowry again plays a young supergenius.
- Adults Are Useless: Granted, there were adults in the house when the parents leave for a wedding.
- Alpha Bitch: Ashley.
- Big Eater: Cat, once her younger body enables her to eat foods that her old age kept her from enjoying.
- Belligerent Sexual Tension: Cat and Gene in spades.
- The Casanova: Gene. No less than an hour after becoming young again, he gets the number of a woman who helps him after Terrance and his friend run into him on their bike.
- Dance of Romance: Cat and Gene go to a swing club and finally relieve some of their sexual tension.
- Divorce Is Temporary: Cat and Gene, though estranged for years, are back together by the end of the movie and are even planning another wedding!
- Evil-Detecting Dog: Gypsy can tell right away that it isn't Sydney walking downstairs. Cat gets chased out of the house because of this.
- First Girl Wins: Although Gene was only dating Ashley to make Cat jealous, it was pretty clear he would eventually fall for her again.
- Identical Grandson: The Mowry twins play the role of not only Willie's sister, but the younger version of his grandmother.
- Impossibly Mundane Explanation: What Sydney reverts to when her long-winded explanation of her grandparents' accident doesn't suffice for Julie. Sydney then says Oprah helped her find her long lost twin, to which Julie asks, "Why didn't you just say that?"
- I Miss Mom: One of the reasons Sydney is so angry at the world is because of her deceased mother.
- Jerkass: Ashley. She denies Sydney a spot on the cheerleading team, tells her she can't date her brother (for some reason) and then when the grandparents are essentially about to die, prevents her and her family from leaving to get them help just because she thinks Sydney is trying to talk to Gene. That punch in the face, for most, was justified.
- Jerkass Has a Point: When Todd asks Ashley why she doesn't like Sydney, she responds, "I smell an attitude problem." Though Ashley is far worse than Sydney, she isn't lying. Sydney spends the entire movie pissed that she doesn't live in LA anymore. She even snaps at Todd for trying to make amends after she gets dissed by Ashley. Granted, she was about to apologize before Terrance showed up, but her bad attitude renders her unfriendly although she manages to make one at the convenient store where she works. Then there's the way she treats Monique, who doesn't appear evil at all. But this could all be attributed to her teenage Wangst.
- Lampshade Hanging: After Terrance tries and fails again to woo Sydney, his friend sees her and asks, "Hey, you got a sister?"
- My Sister Is Off-Limits: Inverted. For some reason, no one is allowed to date Ashley's brother. She makes this clear to Sydney in the third act.
- Police Are Useless: The cop who stops Gene after he suspects he stole his father's car doesn't even bother to chase after him once he runs away.
- Pretty Fly for a White Guy: Terrance.
- Pronouncing My Name for You: Ashley mispronounces Sydney's name at the cheerleading tryouts. Sydney wastes no time in correcting her.
- Secret Test of Character: Turns out Cat and Gene divorced over a job opportunity in Australia. Cat didn't want to go with him and thought if he loved her, he'd stay.
- "The Reason You Suck" Speech: Sydney delivers one to Cat after she catches her dancing with Todd.
- Violence Really Is the Answer: After Ashley tries to keep the family from getting the grandparents help, Sydney delivers a well-deserved punch to her face.
- What the Hell, Hero?: Seriously, why did Cat dance with the guy that Sydney has a crush on?
- Wicked Stepmother: Sydney views Monique as this, though she seems genuinely interested in becoming a part of the family. Cat even tells her to call her "mom."