What age stage does youth refer to?

Youth means beautiful youth, beautiful years, and is generally used to refer to people in their youth. This word is a beautiful praise for youth, and it is very artistic. Youth is beautiful, but people grow up day by day, lose the innocence and gentleness of childhood, and gradually learn to be a steady self. No longer as delicate as a child, but learned to be a patient and tolerant self. At the same time, I won't cry because I lost a beloved toy, and I won't be sad for a little everyday things. When people grow up, they gradually understand what courage is, and begin to realize that life should be a history of struggle, and they need to make progress little by little to spur themselves. Therefore, to grasp youth, only the youth who has sweated will have no regrets.

Youth is a beautiful youth and a beautiful time, which is often used to describe people's youth.