If you are a highly motivated person who also has a business sense and knows what you want to do, you can go far, very quickly. But for most people, motivation is short and needs to be fed. A constant supply of ideas and projects and motivational like-minded people around you, helps a lot.
There is a mountain of websites giving you tutorials (for free even) online. For example: Creativelive, Skillshare, etc etc...where people like you fulfil projects designed by online mentors and then you all have a chat about each other's work and get great critique in order to improve your skills.....
Never discount the opportunity of a wealth of knowledge and tutoring which can be given to you by experts in their field (whether through college or professionally).
If later, you find work alongside a team of graphic designers, they will inspire you, BUT!!!!! you need to get to that stage first and my advice for you is to gain knowledge of the industry and practice practice practice your skill, to build up a portfolio of good work. College worked for me, big time. I wouldnt be in the position I am now if I hadnt taken the plunge into doing graphic design at University. It helped me to build up a portfolio very quickly.