Countries get old fast, here is a fertility rate of 1 (higher than South Korea):

Year 0: 100 newborns

Year 20: 100 twenties, 50 newborns

Year 40: 100 forties, 50 twenties, 25 newborns

Year 60: 100 sixties, 50 forties, 25 twenties, 12 newborns

Year 80: 50 sixties, 25 forties, 12 twenties, 6 newborns

Year 100: 25 sixties, 12 forties, 6 twenties, 3 newborns

Year 120: 12 sixties, 6 forties, 3 twenties, 1 newborn

We are nearing the midpoint of this in many parts of the world. Labor and GDP be gone.