Welcome to the forums, man.

Let's start with your goals - you want to eventually become a level/environment designer? These are viable job opportunities, but you're really selling yourself short if you're limited to some basic worldly objects. You're going to have to possess one seriously impressive portfolio if the only thing you're willing to offer is environments. You might not care for character modeling, but theoretically you should be well-versed in your 3D software enough to produce any type of "object".

Presentation is everything. You can't walk into a studio looking for a job with a bunch of gray shaded renders. You need fully realized and developed images. Look at some professional architectural renders, or any photorealistic 3D interior. Beneath it you'll usually find some relatively simple geometry and wireframe foundations. Take away all of the painstaking touches in the rendering process and you've got a seriously unimpressive image to show off.

Take your computer desk - right now it's a bunch of differently scaled primitive boxes organized to resemble a desk. It's basically something anyone could have produced with a 3D modeler within about 5 minutes. I'm not trying to belittle your work, but the fact remains that to land this sort of job, you're going to have to show that you have the ability to fully realize a living and breathing world from pencil paper to the last few seconds of rendering.

An employer isn't going pick you from thousands of others if all you can do is construct some polygons. A studio won't hire a 3D modeler who only possesses skills that fit into one small portion of their work pipeline. They take someone with a wide variety of skills and then plug them into the pipeline. What I'm saying is, you can't expect to make it simply by being capable of taking someone's concept, turning it into some polygons, and passing it along to someone else to texture it and render it. You're only 18 and have plenty of time to develop an enriched understanding of the whole realization process - and I guarantee your goals and opinions change (even if only a tad) within a year of modeling.

Hay there, welcome to the forums...

One of the first things I was taught on my uni course was that simple modeling of things that exist is not art. We were strongly encouraged to study famous artists and develop our own feelings about artistic styles. You see, given a bunch of measurements anyone could make a human model, infact a scientific mind would probably be better than a creative mind. But it takes real artistic talent to portray a fictional character or location based on concept sketches and design documents. For now its great to get experience in your 3D app, but you should aim to be an artist, and not just a copy cat.