Well...I think it depends on the culture. Where I'm from, these mark important steps in growing up. You usually start school when you're five. Thirteen is the first "teen" year. Sixteen is suppose to be big because it is kinda like...becoming an adult? You can make big decisions then, but not all of the big decisions. Eighteen is when you're legally considered an adult, and twenty-one is when you can legally drink alcohol.

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But that's just where I'm from. Some places let you drink alcohol at a younger age, and in Spanish culture, fifteen is the same as our sixteen.