There is the DC-7 operating on a Part 135 certificate (non-sked airline) in Florida now (the Eastern one) and it's doing a pretty good trip this spring out into the Caribbean. There's also the Air Chatham's DC-3 operating scheduled services in Australia, several additional DC-3's in the US and Canada (Buffalo Airways being the largest operator), so it's not the "oldest", but the Tu-134's are certainly among the oldest jets.
Not to mention her younger sister, the Tu-154 is being grounded en-masse due to the recent rash of accidents, so its even more of a statement that any Tu-134 is still flying.