Can’t Install 301 Redirects Plugin, Fatal error, WP 3.9.3, PHP 5.4.34

I have to semi decommission an old WP website and want to redirect most of the content pages back to the root / homepage. The site is running on WordPress 3.9.3 and PHP 5.4.34.
I have tried to install 2 redirect plugins but both fail to install/run:<br><br>
I’m reluctant to update the WP and PHP versions in fear of breaking the site theme and or other functionality.<br>
301 Redirects plugin should work according to the version specs.<br>
How to install a redirect plugin or apply another method?

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