Perl 5.20.1 for Ubuntu 14.04
You can use perlbrew:
sudo apt-get install perlbrew
Then:
perlbrew init
perlbrew install perl-5.20.1
There will be no version upgrades for Perl (or most other packages) within a single Ubuntu version, because that might break existing code. Instead they will port essential fixes back to the version they ship.
If you want to have a newer version you can use perlbrew to install it, but this will not replace the Perl version shipped with Ubuntu, will not affect any installed scripts and will not use already installed modules.