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Why do we support older versions?
We strongly recommend the latest versions of PHP and
MySQL, but we understand that this isn’t right for
everyone, and that sometimes hosts can be slow or
hesitant to upgrade their customers since upgrades to
PHP and MySQL have historically broken applications.
Note: If you are in a legacy environment where you
only have older PHP or MySQL versions, WordPress also
works with PHP 5.2.4+ and MySQL 5.0+, but these
versions have reached official End Of Life and as such
may expose your site to security vulnerabilities
Source: https://wordpress.org/about/requirements/