Here's something else to think about:
Any "Flight Simulator" aficionado could have flown those planes into those buildings. Once airborne, flying an airliner (with total disregard to safety & standards), doesn't take much skill at all. On the other hand, flying an airliner through all of it's phases of flight (takeoff, climb, cruise, descent, & landing), and doing so safely while operating within the constraints of the National Airspace System, Federal Aviation Regulations, Aircraft Operators Manual, & company policy is very difficult.
There are many different variants of the B-707, some with lower max. takeoff weights & some with higher max. takeoff weights than the B-767-200ER. So, exactly which B-707 were the WTC's designed to withstand an impact from? Even if the WTC buildings were designed to handle a direct hit from a B-707, what speed was it assumed the B-707 would be going? Throughout history, several structures were supposedly designed to meet a certain standard, yet later on were determined (usually after failure), to have never met those standards, or could no longer meet those standards due to maintenance & upkeep practices.