It really depends on the state of the airline industry. The US aside, the industry in other countries had been booming up until the latest economic woes. Even then, the Australian industry has stagnated a little but there is still a lot of demand for pilots in the long term.
It is possible, but unlikely, to have an airline job within a couple of years of starting. There are still airlines like Qantas that offer cadetships where they take kids off the street and put them through the required training.
Normally, if funding isn’t a problem, it might take six months to do your initial training, commercial license, multi-engine instrument rating, and air transport license exams (the license itself isn’t required until later.) Then you might need to do a year or two flying light aircraft gaining a little experience, then you should be able to get a turbo-prop job and after a year or so of that you would qualify for an interview with a major airline. So realistically 3 - 5 years from starting to sitting in the cockpit of a B747, if you’re lucky, have the funds, and are good enough.
There are so many variables though, some people never make it, others may take 15 years. For it to be a viable terrorist option you’d want to start out with lots of students in the hope that one might get there. The other problem is that you’d be one person against the rest of the crew.