India is regarded as a country with a "Demographic Dividend" due to its high population in the age group of 15-64 years.

Demographic Dividend refers to a period of economic growth that can result from changes in a country`s population structure. It occurs when there is a large proportion of the population in the working-age group (15-64 years) relative to the dependent population (below 15 years and above 65 years). In other words, it is the potential economic benefit that can arise from a shift in the age structure of a population, resulting in a larger workforce and fewer dependents.

India has a relatively young population, with around two-thirds of its population under the age of 35, and a large proportion of the population in the working-age group (15-64 years). This demographic advantage has the potential to drive economic growth by providing a large and productive workforce, increased savings, and investment in human capital.

Therefore, the correct answer is "Its high population in the age group of 15-64 years.