/([0-9]{2,})(?(?{index("0123456789", $1) == -1})(*FAIL))/

##</code><code>##

>perl -wMstrict -le
"my $skip_if_not_consecutive = qr{
   (?(?{index('0123456789', $^N) == -1}) (*SKIP) (*FAIL))
   }xms;
 ;;
 my $digits = qr{ \d{2,} }xms;
 ;;
 my $str = 'a1a11a9129a912a129a112a122a34a345a';
 my @cons = $str =~
   m{ ($digits) $skip_if_not_consecutive }xmsg
   ;
 ;;
 my $q_cons = join ' ', map { qq{'$_'} } @cons;
 print qq{'$str'};
 print qq{  $q_cons};
"
'a1a11a9129a912a129a112a122a34a345a'
  '34' '345'