Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
The Perl 5 porters officially ended support for Perl 5.8 on November 5, 2008. Fortunately, Enterprise Support exists to help your legacy Perl 5 installations cope. Distributions such as Red Hat Enterprise Linux and its offshoot CentOS will continue supporting old versions of Perl 5 for up to ten years since their release (the release of the distribution, not the release of the version of Perl 5 they distribute).
For example, the most recent CentOS release, CentOS 5.6, includes Perl 5.8.8. (CentOS 5.6 came out just over a month ago. Perl 5.8.8 is seven stable releases out of date.)
In seven years, when CentOS 5.6 reaches the end of its supported life span, Perl 5.8.8 will have been unsupported by Perl 5 Porters for nine and a half years, and will be thirty five stable Perl 5 releases out of date.
But it's supported and it's enterprise, so the CPAN authors of 2018 must be sensitive to the needs of their users, and so the earliest you can rely on Perl 5.10 features.