Consumers grow an economy by spending on goods and services. Especially spending on 'goods' because these have to be made. Even better if the goods are made in the economy where consumers are spending.
The peak age range for consumer spending on goods is between the early 20s to early 40s.
The more people an economy has in the age group the better it will grow, even allowing for other factors - like the loss of British manufacturing to China for example.
