Final answer:
The mean age of 74 for a group of respondents from the Pew Research Center survey likely corresponds to the 'Ages 65 and older' category, which is part of the young-old life-stage subgroup as per US categorization.
Step-by-step explanation:
Based on the information provided, there is no direct data from a Pew Research Center survey in 2009 indicating the mean age of 74 for a specific group of respondents. However, we can deduce that the mean age of 74 would most likely fall into the 'young-old' category described as individuals who are approximately sixty-five to seventy-four years old. According to the categorization of older adults in the United States, this age range would correspond to option 2) Ages 65 and older. The young-old life-stage subgroup is generally considered as being happier, healthier, and financially better off than in previous generations. This aligns with the overarching trends of an aging population, where the number and proportion of older adults are increasing, as indicated by the research charts and tables provided.