Definitions of generations are not necessarily agreed upon. If you want to use generational research or stats, it’s important that you understand the source definition. I’ve started the embedded chart to show how different studies can have varying definitions, even in studies completed by the same company (case in point GfK). Some sources are pretty similar, especially for the well-established generations, but others can vary by 10 years. If you plan to pull research from multiple places, just be aware that if the definitions vary too much you may run into inconsistencies. Choose your sources and your supporting information thoughtfully.
SOURCES
The Census Bureau
Census does not typically break anything into generations. When people use Census data for generational research they assign Census age ranges to fit their generational definitions. However, Census does refer to Baby Boomers from time to time as people born between 1946-1964.
Harvard Joint Center for Housing Studies
In this article from 2012 by George Masnick we are provided a different method of looking at generations. While Howe & Strauss looked at shared coming-of-age experiences, Masnick shows us another way to look generations — just by sheer birth rates. A bit like a scree plot.
IPSOS Public Affairs
Research done by IPSOS in June 2014 provides a definition for Millennials. Other generational breaks are unknown at this time.
MarketingProfs
This article from 2012 by Tim Hare provides marketing tips to reaching Gen Y (born 1982-1994).
National Chamber Foundation
The Millennial Generation Research Review of research from 2009-2012 compiled by the U.S. Chamber of Commerce provides a handy definition chart in the introductory section of this 40-page PDF.
Neil Howe & William Strauss
The header links their Wikipedia page. The have written several books on generational differences as well as one specifically on Millennials, the term of which they coined.