I am currently selling one plugin through CodeCanyon which supports versions 5.3 onwards, but its becoming harder and harder to keep the plugin up to date (especially its dependencies) while keeping support for older PHP versions. So here’s a two part question: Is there a minimum PHP version projects should support that is required by CodeCanyon ? If not, what do other authors support?
If you not have special reasons to maintain retro compatibility with the older php versions the 5,3 as min version is more than enough
WordPress.org recommends PHP 7.0 since the end of 2016. PHP older then 5.5 is no longer supported by PHP developers and old versions can be considered a security risk, considering they will not get any updates in the future. So, PHP 5.5 should be minimum safe version to use. But, there are users with PHP 5.3, 5.4 and even 5.2, but their numbers are getting lower.