"so all I will have to do is flight train"
That is funny. Yeah, as soon as your done with your flight training you should be good to go to get on with a major.
You have much more to do then the flight training. After you get all your ratings, you will have to build time to get to a regional. A lot of people instruct to get this time, while others find jobs at 135 flying right seat and then to the left seat once they have enough hours.
Then, you should get on with a regional some time... build your time in the right seat and then hopefully pass the training to upgrade to Captain. Now you will fly a few years as Captain, trying not to bend any metal or create any unnecessary paperwork.
Then, if you are dedicated, and lucky enough (yes, there is PLENTY of luck in the timing of getting to a major), you will get an interview at a major. Competition at this level is stiff, but hopefully you will get the job.
So, you have a lot more to do then just the flight training. Put that thought as far out of your head as you can. You are about to enter the world of aviation, it is a great place, but there are a lot of ups and downs. Ups - your first solo, your private, soloing your first student, getting your first regional job, upgrading to captain, etc. downs - failing your checkride, failing your medical, failing your captain upgrade, not getting hired, having an incident/accident, etc.
Your goal to make it to a major is a great one. I think more people should have that as a goal, instead of settling with a regional job. But it is a long road.
As far as years go, we will have another prosperious time in major hiring sometime in the next 8 years... that is without question. So if you can ready yourself, you can get an interview.
In my opinion getting on with a major is 90% who you know and 10% what you know, others may say different. Knowing people can help you get the interview, knowing yourself and your stuff can help you pass the interview.
Don't worry, as you go through aviation you will meet many people, and make many friends. Some of these friends will continue on to bigger and better things. One of the things I have discovered about the aviation industry is that most airline pilots know the hardships one must face to land a job, so most of them will try to help. I have had airline pilots I don't even know offer me advise on career planning. Why do they do this? Because someone helped them, and they pass it down.
Anyway, sorry to ramble. But yes, 8 years is a reasonable goal.
Good luck.