Theme check plugin criticize all and everything, you can try it with every premium theme, there are always hundrets of warnings.
We checked the theme right now and there are “warnings” because the theme offers things like post types, shortcodes and other features, but that’s never a problem with the PHP version or PHP functions.
We tested the theme again on a server with PHP7 and on our end it was running without any problem.
Have you installed plugins? Trust me, over 90% of all problems are caused by plugins, the first thing I would check are always the plugins…