The fact that you say you "know" you will do anything in this industry shows that you have a lot to learn. When I was an FO, I found the captains that had never been CFIs were the most difficult to fly with generally. They tended to micromanage much more than those who instructed. I only instructed for about 500 hours but I found that it made me a better and more patient captain after I upgraded.
There are young 20 something cadets in training here with ANA but I guarentee you that Gulfstream will not give you anywhere near the quality of instruction that any major airline cadet program gives. And you do realize that other 1900 operators actually employ and pay people money to fly in the right seat right?
There is much more to 121 flying that just seniority. Right now with your attitude, it appears that you are going to be "that guy" that everyone dreads flying with. Hopefully that will change when you get some experience. Good luck getting to FDX....There are 1000's of others that have been trying for a looooooooooooong time. It is hardly guarenteed.