I confess to being confused by the use of map here and scared by the apparently endless loop, which probably means i haven't understood something. Here's how i would do the main bit, anyway:

for (@sortedbus) {
    push (@oldbus,$_) if (m/^(\d)+?/ && make_nasty_date($1) < $today);
}
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Which should give you a sorted list of the right files in @oldbus. make_nasty_date is standing for whatever mechanism you're using to convert yyyymmdd into seconds-since-epoch, assuming that's what you're doing.

ps. i expect there are a hundred things wrong with the regex, so let's say it's assuming filenames in the right format.