Thresholds are applied to prevent anyone viewing a report from inferring the demographics or interests of individual users. When a report contains Age, Gender, or Interest Category (as a primary or secondary dimension, a data comparison, or as part of a segment in Analysis), a threshold may be applied and some data may be withheld from the report. For example, if there are fewer than N instances of Gender=male in a report, then data for the male value may be withheld.
These thresholds are system defined, and you cannot adjust them.
If a threshold has been applied to a report, you will see a notice below the report title.