Passing a 15-year-old as an adult isn't exactly a new phenomenon in television and movie culture, but the so-called teenagers' real ages in 13 Reasons Why have caused quite a stir with their much older-looking appearances.

The American drama-mystery series adapted by Brian Yorkey for Netflix, and famously executive-produced by Selena Gomez, centres around a student named Hannah Baker who commits suicide after suffering a series of demoralising circumstances triggered by fellow pupils.

A box of cassette tapes recorded by Hannah before she killed herself details 13 reasons why she ended her life, and some of the show's graphic scenes have left viewers disturbed.

But what baffled viewers throughout the emotionally exasperating series is the real ages of the actors that were meant to be playing high school teenagers.

Let's take a look at how old the cast actually are.

Dylan Minnette, who plays the level-headed Clay Jensen, has already had a colourful acting history starring in the likes of Don't Breathe and Goosebumps – all at the ripe age of 20.

@theellenshow

A post shared by Dylan Minnette (@dylan_minnette) on

Tragic Hannah Baker, who is played by newcomer Katherine Langford, is an Australian actress and former swimmer and is aged 21.

[internally screaming.]

A post shared by Hannah Baker (@itsmehannahbaker) on

Christian Navarro is an American actor enjoying his first breakthrough role in the Netflix show and is 25 years old.

Alisha Boe is a Norwegian-Somali actress and plays Jessica Davis in the show – she is 20.

On a date with a sad plantain

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Brandon Flynn is the popular jock Justin Foley in 13 Reasons Why and is 23. He once played Mr Smee in a musical version of Peter Pan.

Justin Prentice stars as Bruce Walker and is 23.

When you're trying really hard to be sexy, but you're wearing a clip on bow tie... @bradley206 #bowtiesarecool

A post shared by Justin Prentice (@justin.prentice) on

Miles Heizer is Alex Standall in the show and is 22 years old. His most notable film appearance to date is in the 2007 movie Rails & Ties.

You need friends. Even just hot chocolate friends.

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Ross Butler, known for the Disney Channel series KC Undercover, is 26 years old.