Google Analytics for Octopress hasn’t integrated the latest update to include Demographics and Interest reports. In Octopress, Google Analytics code resides in source/_includes/google_analytics.html
According to Google, one line change will include the demographics and interest reports to your analytics. Following is the diff of my source/_includes/google_analytics.html
Just replace the line
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
ga.src = ('https:' == document.location.protocol ? 'https://' : 'http://') + 'stats.g.doubleclick.net/dc.js';
And you are done. It will take upto 24 hours for the new reports to start appearing.
I have opened a pull request for this upgrade. If this gets merged, these reports should be included by default.