PHP 5.6 and PHP 7.0 End of Life
As of December 3rd, 2018, PHP 7.0 reached its end of life. This means it no longer has security support and could be exposed to unpatched security vulnerabilities. Following suit, as of December 31st, 2018, PHP 5.6 also reached its end of life. This officially marks the end of an era for PHP 5, as the first version, 5.0 was launched 14 years ago.
According to the official WordPress Stats page, as of writing this, over 63% of WordPress users are still on PHP 5.6 or lower. If you combine this with PHP 7.0, a whopping 82.8% of users are currently using PHP versions that will no longer be supported come January 2019.
As of late 2016, WordPress.com has been 100 percent switched over to PHP 7. Starting mid-2017, WordPress will officially recommend its users bump versions from 5.6 to 7.0, meaning PHP 7 could become the minimum requirement for running self-hosted WordPress in 2017.
We encourage you to speak to your web developer or web hosting company to request that they upgrade your website to use PHP 7.2 as a minimum to ensure security and support.
With the release of PHP 7.2 and PHP 7.3 came huge performance gains! So big in fact, that it should be a priority over a lot of the small optimizations you might playing around with on your website as well.
See https://kinsta.com/blog/php-versions/ and https://wpengine.co.uk/blog/get-ready-for-php-7/ for the full articles about this.