Japan is too old to have any significant growth:
Japan: 0-14 years: 14.3%; 15-64 years: 66.7%; 65 years and over: 19%
US: 0-14 years: 20.8%; 15-64 years: 66.9%; 65 years and over: 12.4%
China: 0-14 years: 22.3%; 15-64 years: 70.3%; 65 years and over: 7.5%
Now Japan just likes an old saying: 百足之虫,死而不僵.