In 1979, 50 percent of women aged 15-19 and 70 percent of men aged 17-21 living in metropolitan areas of the United States reported that they had ever had sexual intercourse. The average age at which young women had their first sexual experience was 16.2, compared with 15.7 among the men; women tended to have their first intercourse with a partner nearly three years older than themselves, whereas men had their first intercourse with a partner less than one year older. Blacks generally experienced first coitus at a younger age than did whites. Young women's first coitus generally occurred with someone toward whom the respondent felt a commitment; more than six in 10 young women said they had been going steady with or engaged to their first sexual partner. In contrast, fewer than four in 10 young men said that they had been engaged to or going steady with their first partner, and more than one in three said that they and their first partner had been friends. Young men were more than twice as likely as young women to have had first intercourse with someone they had only recently met. Seventeen percent of the young women and 25 percent of the young men surveyed said that they had planned their first intercourse; women who had been going steady with their first partner were most likely to have planned intercourse, while the young men who had met their first partner shortly before intercourse took place were the most likely to have planned the act.(ABSTRACT TRUNCATED AT 250 WORDS)