Clarke's age has no simple answer. After all the events of The 100's 7 seasons, Clarke's mental, physical, and chronological age are all different.
Clarke Griffin goes through so much in The 100 that it’s not easy to say how old she is by the end of the show. Starting out as a teenager, Clarke goes through so much during the show’s runtime that it would make anyone seem older than they truly are. The science fiction elements over 7 seasons of The 100, however, mean that Clarke ends the series older than she looks in a very literal way.
Based on a YA book series written by Kass Morgan, The 100 puts a unique spin on the post-apocalypse narrative after a group of people survive the end of the world by being in space when it happens. The CW’s TV adaptation follows a group of one hundred teenage delinquents who are the first to return to the ground since the apocalypse 97 years earlier. Very soon, they encounter the grounders, descendants of those who survived the apocalypse down on the surface. At the time, the year is 2049, and Clarke is 18 years old.
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By the final scene of The 100, Clarke is physically 25 years old, but her physical age is not the same as her chronological or mental age. The plot involves sci-fi technologies like mind drives which can add years of experience to a single person, and cryosleep chambers which allow people to survive in suspended animation for extended periods of time. During her run as the main protagonist of The 100, Clarke uses both.
The 100 begins in the year 2049, with seasons 1 and 2 following each other in succession. 86 days after season 2 ends, the events of seasons 3 and 4 begin, in 2050. The tumultuous climax of season 4 of The 100 sees Clarke left alone on Earth after praimfaya scorches the planet. Over the next 6 years, she meets and adopts Madi as her daughter, making a home for them both in Shallow Valley, until the world’s 3rd apocalypse destroys it at the end of season 5. Following this, in the year 2156, all the surviving humans board the mining ship, Eligius IV, and Clarke enters a cryosleep chamber. The events of seasons 6 and 7 take place 125 years later, in the year 2281. By the end of The 100 season 7, 150 years have passed in real time since Clarke was born.
Clarke’s most uncertain age, however, is her mental age. During the finale of The 100 season 3, Clarke takes possession of the Flame, a device sacred to the grounders, used by their Commanders. The 100 establishes early on that the Flame contains the memories and experience of every previous commander who took possession of it before. It’s unclear exactly how many Commanders’ minds it contains, so a little guesswork is needed to work out what effect it may have had on Clarke. The first to use the Flame was scientist Becca Franko, who only used it briefly before her death at the age of 29. It’s heavily implied that the Commanders don’t tend to live very long in such a brutal world so, assuming a new commander is chosen by the grounders every 10 years or so, the following 95 years probably saw 10 different commanders after Becca, each being granted the Flame at around the age of 12. All of this means that when Clarke briefly takes the Flame herself, it temporarily gives her 244 years of combined knowledge and experience, from the lives of everyone who’s held it before. During the season 3 finale, the Flame boosts Clarke’s mental age to 263. It’s impossible to say how much, if any, of that is retained after the Flame is removed from her.
A huge amount of chaos and turmoil ends up being thrown at Clarke Griffin by The 100 over 7 seasons. The main conflict of her character is that she’s forced to grow up too fast, taking responsibilities she isn’t ready for, and suffering the consequences of actions she should never have needed to take. Starting out at the age of 18, she’s physically 25 at the show’s ending. At the same time, she’s chronologically 150 years old and, briefly, her mental age peaks at 263.
