I'm 16, however, I have quite a lot of connections in the industry.
I've worked for one of the Top 10 UK Agencies outside of London during summers before as a Junior Web Designer. Most of the design team I worked with all had a Graphics Design Degree, one didn't.
The one that didn't, was the lowest paid, and the hardest worked. He went about how he did things differently. He had worked his way up the ladder. Due to the fact of his lowish pay, he was actually moving to London to do freelance work, because he would earn more there, even though he could probably never move above a "Middleweight" designer, as he wouldn't be recognised without that bit of paper.
The most valuable thing they taught me about making a portfolio/trying to get into the business etc etc, is ideas. They said the company wants to see your thought process, the idea's behind the design, how the user feels etc etc. Because this then shows the thought in your Design and it also helps you develop the end product.
Design as much as possible, do sketches, scribble little notes, scan it aswell as sticking it onto Paper so you have a hard Portfolio aswell as a Website.
If you're really clever, you can use your little sketches and scribbles as part of your site design
Hope this helped.