Actually, the fact that you are asking this question show real maturity for a 17 year old. It is a fundamental question to ask before you invest hundreds of hours in an activity.
I can't define your aim, but hear is my analysis as a 43 year old guy that has been riding for 20 plus years.
First, I love riding 2 wheeled vehicles whether motorcyle, road bike, or mt bike. I love the feel riding and feeling the wind. I love how everything looks different on a bike. On a road bike, I like the silence and speed together of watching the world go by from a perch on my seat. On a mt bike or dirt bike, i love having to negotiate over obstacles and seeing that side of the world. I love the sense of accomplishment I get from getting through some tight stuff, and the sense of adventure. I love leaning to turn, standing on pegs or pedals and boucing down single track. There is very little I don't love about being on any kind of bike. Over the years, I have seen breathtaking scenery on a bike. From riding in a fast group through rush hour around a busy city to being alone on a country road and watching an amish farmer plow his fields with a horse, I have seen all this and more on a bike.
Second, I like riding with other people. I love being in a group, the mini races that develop over the course of any ride where there are more than one rider. I love the conversations that develop when you are out riding at a more relaxed pace. I love needling my buddies about their weaknesses, and getting needled about mine. I love the trash talk that develops over email chains for days after an epic ride. Over bike rides, I have heard my riding buddies share things as wonderful as expecting a new baby, and as tragic as a divorce or the death of a parent. I have certainly shared some happy and sad stuff over the years. Planning trips around a bike have also played important roles over the years as well as the feeling of comraderie that comes with the trip itself.
Third, in order to enjoy and participate fully in One and Ywo above, I train. I want to be the first guy up a hill. I want to be able to enjoy riding by myself at a comfortable pace. I want to make my buddies suffer on a long ride; and want to be good enough that I can ride with guys that make me suffer. That means hours on a trainer sometimes when it is tough to rememember the joy I experience doing One and Two.
Fourth, I like being able to fit into the same clothes I wore in HS; participate in a touch football game and still be in shape, and have my wife not look at me like I am some disgusting beast. To some extent, this could happen doing any number of exercise related activities, and I supplement these benefits from other cross training pursuits, but they are great benefits that come from doing something I like doing anyway.
Finally, if you are young. I have seen some folks develop a passion for running, lifting weights, martial arts, golfing, tennis, softball, etc. But it is good to have a passion for something beyond work, school, or your family. Finding your passion might involve trying many activities on for size before you find yours. I don't begrude anyone from digging a passion that might be different than mine. For business, it would be easier if I enjoyed golfing because there is a lot of business I miss out on that is discussed on the golf course. For spending quality time for my wife and other couples, tennis would be better. But I just don't feel the same passion for either of those activites. For me, if it has two wheels, I can figure our a way to have a lot of fun on it; and I will be sweating and tired using it, even if it has a motor. And, nothing beats a road bike for just being able to roll out of your garage or house, and enjoy it almost from door to door.
Good luck. And there have been times when for many reasons, riding has been less pleasurable for me than other times. And I have certainly invested in other activities from wrestling as a coach and wrestler, to boxing and karate at fairly high levels of competition. But I just have more in common with the folks that I have met riding, and enjoy riding more now than some of the grappling and striking sports that were more fun when I was younger and healed faster.
Find your own gig. If it is cycling, you will regain the passion and training comes naturally. You will certainly have down times though even in activities you are passionate about.
