The Danza: Ryan Matthews is played by Ryan Eggold.
Riley is played by Riley Smith.
Dawson Casting: In the extreme, to the point where this trope is often called "90210 Syndrome" outside of this wiki, since the extremeness makes Dawson's Creek look like they cast age-appropriately.
Though there were some aversions (Brian Austin Green, Tori Spelling, Jennie Garth, and a few others), the straight examples were very extreme (Most infamous was Gabrielle Carteris who was twenty-nine when she started on the show and in her mid-30s when she left it.).
Directed by Cast Member: Jason Priestley directed 15 episodes, James Eckhouse directed three episodes, Jennie Garth directed two episodes, Luke Perry also directed two episodes, Brian Austin Green directed an episode, Tori Spelling also directed an episode, and Ian Ziering also directed an episode.
Dye Hard: Silver is a natural blonde as shown in the parent shown, but is a brunette for the entirety of the series save for when she briefly dyed it red.
Executive Meddling: Season two drops Ethan and focuses a lot more on the new characters rather than the old cast. That's cleverly done for Kelly's mother's funeral as it's not shown and Silver comments that a lot of people that knew her but she didn't know attended.
Fake Brit: Blair Redford who plays Oscar is not British.
Fake Nationality: Michael Steger is a mix of several nationalities but Iranian(or anything Arabic) is not one of them.
I Am Not Spock: Jamie Walters actually hated his role as Ray Pruit, Donna's abusive boyfriend, claiming that the character was impeding his potential music career by making people refuse to buy any of his albums or concert tickets on the grounds that they actually thought he was like Ray in real life.
The Other Darrin: Rather than bringing back Mercedes Castner to play Silver, she was played by Jessica Stroup.
Reality Subtext: The Sequel Series had a particularly harrowing example for Anna-Lynne McCord. During filming of the scene where Naomi is raped, McCord's castmates simply thought that she was a really good actress, not knowing that she had actually been sexually assaulted herself when she was eighteen. Her breakdown and tears during that scene? She wasn't acting — she was having legitimate flashbacks to her rape.
Unintentional Period Piece: This was the first of the many, many iconic teen dramas of The '90s, and the first of many to fall into this trope. It also does a great job at keeping up with the times. Season one looks straight out of the 80s while season five and later look straight up 90s.