我的少年长大了我的姑娘懂事了
[wŏ de shăo nián zhăng dà le wŏ de gū niáng dŏng shì le]
Depicting coming-of-age, it refers to maturation—boys becoming responsible men (young people) and girls growing wise beyond their years as well-mannered, knowledgeable women. There’s also an undercurrent of nostalgia or pride from the narrator.