By age 65, what percentage of adults are grandparents?

The percentage of adults who are grandparents by the age of 65 can vary significantly based on cultural, regional, and socioeconomic factors, as well as personal life choices. As such, there's no single percentage that universally applies to all populations at this age. In many Western countries, it is common for a substantial proportion of adults to become grandparents by the age of 65. In the United States, for example, studies and surveys have suggested that upwards of 50% of adults may be grandparents by the age of 65, and the numbers might be higher or lower in other regions or groups.

It is important to recognize that these figures can fluctuate over time due to changes in societal norms, like average ages at which people have children and life expectancy. To get an accurate and current picture, one would need to refer to demographic research or surveys conducted in the specific population of interest.