"Life is what happens while you make plans"
The assumption is that one can make a decision now about the next thirty years. I work in an odd area of corporate aviation and I've meet hundreds of pilots in dozens of departments who were, or aspired to be, airline pilots. But, life, the economy, politics and so on interfered with the best of plans. Wives and families being a big influence. This is true on 6 continents; I've flown with ex-airline guys in South America (Brazilian airline turmoil), Australia and NZ (Ansett's crash) and various pilots in the M.E. Except for 5 years at EAL, not one part of my career went as planned.
Get used to it--it a crazy business that is dependant on someone spending big dollars, liking you to fly it.
The only decision that matters early on is to be be dedicated to really learning the craft of operating planes and being flexible enough to change plans when needed.