The term demographic-economic paradox refers to the inverse relationship between economic progress and birth rates. Education and wealth go up at the cost of birth rates. This has been observed in almost all developed and developing nations. Although countries like China and India have government-sponsored programs to restrict their populations, unbiased population metrics from the Western countries and industrialized Asian nations like Japan and South Korea confirm this.
In my economics and civics classes in high school, India's population growth rates were partly attributed to the farming community's labour-intensive trade, in which more children (especially male) meant more farmhands and therefore more revenue. As agriculture declined as a percentage of the GDP, and agricultural income for farming families began to be artificially kept low in India due to the presence of Government intermediaries and established "fair prices," besides the low per capita land holding that has been established, more children began to translate into more cost and much less revenue. India was one of the first countries to encourage family planning. This came to an undesirable extreme in the seventies when Sanjay Gandhi forcefully sterilized, some say up to a million people, in an attempt to control population growth. For an economy growing at a snail's pace of 2 to 3 percent a year from a poor base, more population simply meant fewer resources per capita and therefore a diminished standard of living. After Gandhi's forced sterilization program met with outraged protests and a change of government took place, the family planning program has been far more benign, playing the role of an advisor and encourager.
China has been another aggressive implementer of family planning, imposing stiff penalties on couples who had more than one child. Many have written about social problems and future economic problems that this has posed or will pose. Other measures like prohibition of gender determination have led to fewer female child abortions lately, but the gender imbalance in both these countries remains sharp.
The US has no such government program but has experienced the decline in birth rates that all industrialized countries have. Unlike some other countries, like Sweden and Norway, which experience declining population growth rates, the US has kept up a rate of over 2 percent due to better population replacement rates internally, as well as through immigration. Even so, the US has an aging population which will be supported by the younger citizens in the years to come. This is especially clear in the case of the Social Security funds which are now being propped up by payments made by those still working to cover the retirees. In 20 years there will be a small section of the population (younger taxpayers) supporting a larger group of aged retirees, meaning there will be insufficient funds in Social Security. This is expected to lead to need-based rationing and/or provisioning of funds, as well as a cut in the percentage of per capita allowance of these funds.
India has a rapid GDP growth rate, as high as 7.5 percent in the recessionary 2009-10 years. China too, has not skipped a beat in its blistering growth. However the economic effects of a smaller percentage of younger population are expected to show up in 30 years. This will mean fewer resources to deploy in critical manufacturing and services for export in which these countries have specialized, less availability of specialized labour to meet the growth rates needed to continue growth, a skewed distribution of labour in several fields and of course, the dangers of a gender imbalance. At present the danger of a small cohort of young people supporting the aged does not seem imminent, as the percentage of younger people is quite high in these countries. One-fifth of the total world population under 20 years of age is in India. As they enter the labour force the opportunities and resources are bound to be stretched, but the market that they represent as consumers in an expanding economy will be sizable.