Though Naruto was carefree and naughty during childhood, once he became more older, became teenagers, he realized a lot of consquences and responsbility of being leader, and being thoughtless can make more troubles.
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After the Shinobi War, Naruto made a huge effort in wining the war. Due to the fact that Ushiha wanted to conquer the entire world, all of Shinobi(ninja) came together, help Naruto because of his excellent skill,to fight against Ushiha.
Finally, once Naruto turned to 18, he became the leader of the villege because of his huge influences that he did during the war, and all of people recommanded him. He achieved his utimate goal of his life.
source from https://www.wattpad.com/282713824-naruto-boruto-toruto-characters