OOP is considered an Advanced Topic in Programming Perl, so does not using OOP imply an Amateurish level of Perl knowledge?
No. I think you are confusing Perl knowledge with wisdom. I've been programming for about 30 years and only learned Perl and OOP in the last 5 or so. The first Perl programs I wrote were non-OOP C-like code, with gastly things like global variables (horrors), but strangely enough they worked and they were solid in production. I've learned a lot since then (OOP, Perl idioms, etc), and I don't write Perl code like that anymore, but I wouldn't call non-OOP usage either Amateurish or Novice level.
A novice is someone that uses what they already know to help them in a new field, knowing they will need to learn more, try new things and that they will make mistakes that will need correcting. An amateur is someone who uses the latest shiny tool (e.g. OOP) when it is inappropriate for the problem at hand, and doesn't suspect a thing.