There are two things to consider:

Security

It is essential to use at least PHP versions that have security fix , that is, even if they do not receive new updates, they have corrected vulnerabilities.

To know the PHP lifecycle, there is an official link with a fairly clear graphic at the following link:

  

link

Using the versions that are still on the chart for the current date, everything is OK. Knowing the end of the product lifecycle helps you to get organized to update yourself in time to take no risk.

Resources

With each new release, new features are added, new features are added, existing features are improved (not always, but expected), and there are usually built-in functionality improvements, increasing speed and stability language (within what the PHP base allows).

Some functions are removed, or marked for removal (indicated in the documentation as deprecated , often translated wrong for "deprecated", which is not the same thing.)

This by itself is no reason to upgrade if you do not really need these improvements. Often the risk of breaking an existing application does not justify the rush to change versions.

For version change, it is advisable to consult changelog and update notes with care, and evaluate where this will affect your applications.

More detailed guidelines for version change are found here:

  

link

By following these guides, you can anticipate and upgrade applications for a quieter change, and then upgrade.

Other components of XAMPP

I'm using PHP because it's the most complex element of the set, but the same reasoning applies to Apache MySQL / MariaDB and any other component.

I would recommend including not to use XAMPP in these cases, but rather to install each component separately, as the life cycle of each is completely different. XAMPP is great for rapid deployment on a development and testing machine.

For use in a production environment, I begin to remember those old TVs that came with a built-in VHS player. It may be practical to install, but if you need to change / fix anything, it gives you more work.

It goes according to your need. I'm currently using the 5x version that is stable.

There are just a few things you should stick to.

For example, in 7x version of php, some functions have been removed.

In the documentation have this example below

class foo {
  function foo() {
    echo 'Eu sou um construtor';
  }
}

In version 7x it will generate the following error

Deprecated: Methods with the same name as their class will not be      constructors in a future version of PHP; foo has a deprecated constructor in example.php on line 3

We also have the ldap_sort() function that was deprecated and mysql_*() that were removed. Of course, there are several changes from version 5x to 7x, however depending on your application, it might not be affected at all.

Update

Versions prior to 5.6 have been discontinued. See more in this link .