I don't know the last sentence of human years.

The previous sentence "I don't know the years" means that the world doesn't know the years. Once the youth is gone, it will never come again, and you will never see the arrival of the next day. Encourage yourself in time, time waits for no one. Time flies: wasting time, wasting time. Doing nothing wastes time. Time doesn't know how cold and warm the world is, and the world doesn't know how fast time passes.