How many years does it take to be an airline pilot?

It depends on what country you live in. It takes about 1-2 years to obtain a Commercial Pilot Certificate if you can train more or less full time. After that it can take from a few months to earn a restricted Airline Transport Pilot Certificate (ATPL) to several years to earn an unrestricted ATPL. With that in your pocket you might be hired by a regional airline but you can expect it to take many more years to obtain enough experience as a working pilot to be competitive for a major airline job. In some countries, like the USA, if you don't also have a 4 year college degree, your chances of being hired are slim to none.

The average pilot hired by a regional airline is about 24-25 and has at least 2-3 years work experience, plus the year or two spent in training training. The average pilot hired by the major airlines is over 30 years old and has 5 to 10 years of additional experience beyond what it takes to be hired by a regional airline.

And no, knowing "most of the stuff" is inadequate. You must know ALL of it and have earned all the required licenses and ratings as well as the preferred or required amount of flight time. There are no shortcuts unless your daddy or one of his close friends owns an airline.

You must complete over 2000 hours of flying before being eligible to be tested.

This takes many years and a lot of money. Flight instructors charge from $ 150. - $300. per hour.

Even then, you are not guaranteed a position.

A lifetime.