The period of adolescence is lengthening in industrialized cultures, such as those in Europe, the United States, and Australia. Adolescents are taking more time to finish their education and establish careers. The average age for a first marriage in the United States has increased more than four years since 1960, to for men and for women.

The average age for a first marriage in the United States has increased more than four years since 1960, to 28 for men and 26 for women.

Explanation:

Around fifty years ago, men and women entered adulthood earlier than they do nowadays in industrialized countries. In such countries, most people enter marriage and parenthood at around the age of 30. In the US, the average is 28 for men and 26 for women. There is a name for this new life stage experienced by people: emerging adulthood. It lasts roughly from ages 18 to 25, and it is characterized by people exploring identities, self-focus, instability, and a sense of endless future possibilities. In non-industrialized countries, emerging adulthood is experience by the middle-class elite, but is expected to grow.

the answer to your question is,

d. when a child was born.

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