What is emerging adulthood, and why do critics argue against calling it a "distinct period of development"?

What will be an ideal response?

Emerging adulthood is the transitional period that extends from the late teens to the mid-twenties in which young people have left adolescence but are still a considerable distance from taking on adult responsibilities. Critics offer a number of reasons why this "emergence" does not actually represent a new developmental period.
First, burgeoning high education enrollment, delayed career entry, and later marriage and parenthood are cultural trends that began as early as the 1970s in industrialized nations, only gradually becoming more conspicuous. At no time has adulthood in complex societies been attained at a distinct moment. Rather, young people in the past reached adult status earlier in some domains and later in others, just as they do today. They also may reverse direction—for example, move back to the parental home to get their bearings after finishing college or being laid off a job. Transitions occur during all periods of adult life, with societal conditions heavily influencing their timing, length, and complexity.
Second, the term emerging adulthood fails to describe the experiences of most of the world's youths. In most developing countries, young people—particularly women—are limited in education and marry and have children early. Also, many low-SES individuals in industrialized nations lack the academic preparation and financial resources to experience an emerging adulthood.
Third, research on emerging adulthood largely emphasizes its personal benefits. But the extended exploration that defines this period may be largely a coping mechanism on the part of young people who cannot find rewarding jobs, even after college graduation. If satisfying work enabling financial independence were plentiful, perhaps emerging adults would not choose to postpone these responsibilities.
Skeptics point out that, rather than being unique, emerging adults are part of a general trend toward blurring of age-related expectations, yielding multiple transitions and increased diversity in development across the adult years.