if (-f && '$_, !~ /^\./' && ($age > $limit)) {
          ^^^^^^^^^^^^^^
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What's with the quotes? This is just a string literal. You might as well have written

if (-f && 'Hello World' && ($age > $limit)) {
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Fix:

if (-f && $_ !~ /^\./ && ($age > $limit)) {
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Or just

if (-f && !/^\./ && ($age > $limit)) {
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Please wrap you code in <c>...</c> tags in the future.