If you're only 18, I would not rush into a fast paced program like ATP (I am a graduate of the program). You have a lot of options. But above all else, at some point in your flying career (i.e. when its time to upgrade from a regional airline to a major), you will need a four year college degree. I would go to school and fly while you are in school. Get your private the first year, instrument the second, commercial the third, and maybe CFI and Multi-engine the fourth year of college. If you could graduate college with your CFI in hand, you'll be set. Instruct, get your 1500 and then go to a regional with a college degree in hand to fall back on. Also, it is recommended you get a degree in a non-aviation field (see prior statement "to fall back on"). With the new regulations, you will not be able to fly for an airline until you are 23 years old (barring a few special circumstances that require an aviation degree from an aviation school).
As a guy who went through the ATP program... Here is some basic information for you to consider if you're still considering going there. Don't let those who say you won't get good instruction at ATP sway you. Yes, it is a pilot mill and there are instructors there that are solely in it for the time build and don't provide the best quality instruction. But this is not the standard. I went to ATP in Richmond, VA in 2013. I started already having my Private Pilot cert which I earned at a local mom/pop shop. I had an excellent instructor for my private training, but I believe my ATP instructor was even better. He was fully invested in my success and the success of all his students. He spent lots of extra time doing ground training (which ATP instructors are not paid to do) and went above and beyond to make sure I was properly trained and prepared in all areas. Disclaimer: If you go to ATP, you must be ready to work you tail off. It is A LOT of self study. A decent-to-good instructor will help you with ground work, but not if you're aren't putting forth the effort and are studying significantly on your own. No one there will hold your hand. It is a VERY intense program that is fast paced. It requires 100% of your attention and focus. But it will get you your certificates quickly.... However, based on your age, you don't need them quickly. You have time, which is why if I were you, I would not go to ATP.
I had a great experience with ATP, but it isn't for everyone. I do not instruct for them... I could not afford what they pay their instructors (its really really bad). I currently instruct for a larger flight school with four locations in Northern Virginia. I am roughly 240 hours away from the ATP minimums and have interviewed with two airlines and secured offers at both. I will start training sometime this summer.
All in all... Go to college. Get a four year degree in an non-aviation related field that will give you options down the road should the economy tank again and pilots get furloughed. Earn your pilot certificates while in school and then when you graduate, you'll be set to be in the right seat of a jet by the time you turn 23. Also, do well in school. Your college transcripts won't be looked at when applying to regionals... But they will be looked at when going to a major airline and GPA matters (so I've been told).
Lastly, be weary of aviation colleges (ERAU, UND, etc...). Not that there is anything wrong with the education you would receive there (though, once again, you should look to earn a non-aviation related degree to fall back on), but they are insanely expensive. ATP isn't the most economical way to do it either, there you are paying for the speed of the program. However, aviation colleges/universities are way, way more expensive.
Lastly, college is awesome. Four of the most fun years of life.... I couldn't image not having gone.
That's my advice. Good luck!
Mike