Updating my post to accommodate the anchors and your update:

my @strings = ('AZ', 'A SOMETHING Z', 'ASOMETHINGZ', 'A  Z', 'A ZZ', '
+AA ZZ', 'AAZZ', 'A Z');

for (@strings) {
    if (/^A( [^Z]*)?Z$/) {
        my $grabbed = $1 // '';
        say "'$_' grabbed '$grabbed'";
    }
    else { say "'$_' did not match" }
}
__END__
'AZ' grabbed ''
'A SOMETHING Z' grabbed ' SOMETHING '
'ASOMETHINGZ' did not match
'A  Z' grabbed '  '
'A ZZ' did not match
'AA ZZ' did not match
'AAZZ' did not match
'A Z' grabbed ' '
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