The announcement from Google that sites need to be responsive was done in February of 2015.
Web developers and SEO providers took note of this, because it is rare for Google to announce algorithm changes in advance.
The change was enacted in April of 2015, and many businesses that still had non-responsive sites were negatively affected in the search engine results.
Is your site mobile responsive?
It's urgent that you make it soon so your site will not be penalised by Google...