You may be able to get them to update to at least 5.18.0 if you tell them about CVE 2013-1667 and all the mitigations added to 5.18.0 to prevent them.

https://duckduckgo.com/?q=CVE+2013-1667&ia=about

http://blog.booking.com/hardening-perls-hash-function.html

I would also recommend reading "Modern Perl" which is made available for free by the publisher/author at http://modernperlbooks.com/

( Also there are large codebases written in Perl ( I beleive booking.com is an example )

I also recommend installing the Perl you are using outside of the system directories. You may also find Pinto and https://Stratopan.com useful for managing your dependancies. Which is especially useful if you make your codebase modular.