Google analytics demographics report displays data about the age and gender of your audience. To view reports in google analytics first you have to enable the demographics and interests reports.
Here is how to enable google analytics demographics report.
Step#1: Enable Advertising Reporting Feature.
Navigate to admin >> property >> tracking info >> data collection
Enable the advertising reporting feature.
Step#2: Enable demographics and interests reports.
Navigate to admin >> property settings
Enable demographics and interests reports toggle and click save.
Once you enable reports you should see reports within the next 24 hours. If you are not seeing demographic reports after enabling then read this.