Excerpt: 'The Millennials are somewhat larger than people expected,' says William Strauss, co-author of the book Millennials Rising: The Next Great Generation. Baby Boomers, born between 1943 and 1960, averaged 3.8 million births a year in the United States, his co-author, Neil Howe, says. Millennials, born between 1982 and 2002, averaged 3.9 million births a year in this country, he adds.