Has someone with no experience at all ever taken off in a plane? Could they?
The Aviation Safety Network has an article listing 11 airplanes that crashed after being stolen by a non-pilot. The most recent was the Horizon Air Dash 8 that was stolen by a ground service agent in August 2018.

There are more interesting stories such as:


The guy that tried to crash a Cessna 150 into the White House (with minimal experience and training)
Ground crew member that stole and crashed an F-16 in Norway
Mechanic that accidentally took off in an English Electric Lightning
Mechanic that took off in an F-86 Sabre
15-year-old that stole a PA-34 and took off with 4 passengers, later crashing


Whether these qualify as "amateurs" is a matter of opinion. Most of them were mechanics/engineers. It would be difficult (but not impossible) for a person not familiar at all with the aircraft to get it started and manage to take off.