Responsive screen with 25 user selectible interests

What is the best way to design a 'user interests' selection screen for a content(ugc and self owned) web app. Its a screen in a WebApp that will be shown to new sign-up users. Expected traffic is largely going to be on mobile devices. Current number of selectable items are 25. May grow to 40 if UX is not affected. My current solution has 24px circle images that grow to 36px on selection with opacity change also. I am getting poor pre-launch feedback. The Webapp mixes food and social domains, so large chunk of target users will not be tech savvy.