We all have to grow up some time, writers and directors also did at one point. Following the basic writing lesson of sticking to what you know, it is a stable theme to explore in movies (and other media).
Coming of age film portrays the time of life when the protagonist(s) grows up, focusing on how he or she matures emotionally. Depicting the psychological and moral growth during the transition of a protagonist from youth to adulthood. Among others themes of self-discovery, sexual awakening and responsibilities vs. the loss of childhood dreams and naivete often play a big role. Protagonists are most often adolescents, although they can also be (slightly) younger or older. Often set in the past during the filmmakers own formative years, these movies are frequently infused with nostalgia.
(more info: https://www.allmovie.com/subgenre/coming-of-age-d959, https://en.wikipedia.org/wiki/Coming-of-age_story)
Half-life = 40
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Perception de Ambiguity (unranked27)
These are our 100 favorite Coming of Age Movies.