There now is a "consensus" of what the minimum version of perl is to be supported for the major modules on CPAN (amongst which is DBI). The consensus today is 5.8.1, with an option to move to 5.8.4 when the need arises.
The fact that a new version of any of those important modules starts using a new(er) feature that will require a newer version of perl does NOT mean that the previous version of the module suddenly stops working.
The module authors are very well aware of OS's that stick to old(er) versions of perl, but sometimes it is hard to stick to cruft to make a module build on those old platforms or OS's. A reason might be that a compiler is buggy. That buggy compiler also does not get updated/upgraded on that old system, so why would you update a perl module that behaves well?.
Once you update the OS, you also probably get a newer version of perl and your problem is gone. If you don't use system perl, nothing is stopping you installing a newer version of perl alongside the system perl.
As most modules have public repositories nowadays, nothing is stopping you to backport bugfixes that affect you to the now unsupported ancient environment.
I for sure do NOT foresee a sharp decline when module authors start declaring 5.8.4 as a minimum.
Enjoy, Have FUN! H.Merijn