Here in the Netherlands there are several ways to enroll in commercial aviation as a pilot. The quickest way to become a pilot for an airline is to go through selections of integrated flight schools, and if you get accepted, in two years time you leave the school with your ATPL theory and CPL. The most of these schools have a good name in the industry, and so have their students, so you will find a job, if, of course, the pilot market if favorable. KLM hardly employed new pilots for the last two years approximately, until recent summer, and now market expectations are fairly good for new graduated pilots. So, if you get through the selections, it depends a little on your luck how soon you get employed. But if you had a good education you will get employed sooner or later. Selections for the KLM Flight Academy can be started at the age of 16 or 17 till the age of 27. So you can go to college or university first. This is the path i've chosen, I'm graduating for my studies now and recently got accepted for the KLM Flight Academy. I am very happy with the fact I studied first, even though I could have gone to the KLM FA straight outta high school. This is basically because my interest goes further than "just" flying. But this a personal choice. I know that for the KLM flight academy high school physics are compulsory, but you can do this as a "stand alone" subject in the Netherlands after your high school. Another way of obtaining a CPL is the modular way, which basically means you get your licences and ratings, i.e. PPL, CPL, IR, ME not necessarily at the same school, you sort of pave your own way. If you do it this way, chances of finding a job at a big airline quickly are smaller, however surely not impossible, again, of course, depending on market demands. These modular obtained CPL pilots usually build experience flying charters, small cargo airlines, instructing, just any kind of flying that gives them enough hours of experience to apply for a job at a big airline. As an example, KLM hires students as first or second officer straight form the flight academy without any experience other than that from the KLM FA, which is about 180 hours (not exactly sure about the exact amount), whereas if you apply at KLM with a modular obtained CPL, you must have something in the order of 500 or 1000 hours multi engine experience (which can be hard to get) (again not exactly sure on the numbers, but it gives an indication). So there are many different ways to many different pilot seats, it can not be said that it is "easy" or "difficult". However, with determination you will get there!
Beware that this goes for the Netherlands, so it may not be representative for another country.
Hope this helps. Cheers.