in reply to What is modern Perl?
Check that the tutorial uses good, modern style. 3-arg open (or at least whitespace between action and filename). Should be advocating 'use strict' and 'use warnings' (which will show it's at least 5.6 or later). Should introduce perldoc very early on. Lexical filehandles. No ampersands when calling functions in the ordinary case. /x both mentioned and advocated for regex. POD. Other stuff. And most importantly, security, including common sense and tainting.
In "Other stuff" above, I'd include a sound Test::More-based test suite (in t/ directory) with good code coverage.
FWIW, I'd say Perl become "modern" around version 5.6, since that is the version that introduced lexical file handles, 3-argument open, and use warnings.