I loved animals and watching National Geographic episodes of Jacques Cousteau made me think it was the coolest thing. 20 years later, I didn't become one, but I have a friend who did.
Marine biology requires you to spend plenty of time at the sea, getting dirty, doing lots of study and research, with plenty of travelling. You have to study various fields besides biology (like oceanography, ecology etc) and be prepared to spend time away from family and friends in the field on more than one miserable rainy day :)
But it's ever so rewarding!!! Oceans have so many hidden mysteries and possible answers to humankind's salvation for many diseases and cures.
To answer your question, you have to ask yourself why? Why do YOU want to be a marine biologist? If it's just because you like animals, it would be awesome to become a veterinarian. But if you go to an aquarium and see the majestic sea creatures calling out to you - I say go for it!
Aravindhan recommends the following next steps:
You should take a marine biology class (if offered at your school). I took the class in my high school. And while I'm not a marine biologist, it was interesting to learn about. That would be the best way to determine if it's something you want to pursue. Good luck!
Courtland recommends the following next steps: