After experiencing the trauma of his mother’s death, Eren, together with Mikasa and Armin, enlists in the 104th Cadet Corps. They are joined with other cadets around their age, notably Annie, Reiner, Bertholdt, Ymir, Christa, Sasha, Jean, Marco and Conny. They are trained by Keith Sadies, who previously was the commander of the Scout Regiment.

Correction

Um actually … Ymir was not the same age as the trio. She was a Titan for around 60 years before turning back to human, so her actual age is over 70.