Question: Can an author write a novel and get it published if he/she isn't a qualified journalist or a writer?
Absolutely. Or, to put it another way, writing is a profession in which the qualifications required to sell a manuscript are simply to have written a good manuscript. I've never seen a publisher's submission guidelines say "Must have degree in writing," and I doubt I ever will.
You can, of course, take an MFA (Master of Fine Arts) program in creative writing. Such programs can give you the opportunity to get regular feedback on your work, make contacts, and learn something of the literary world. They can also force you to dedicate a period of your life to learning the craft of writing, and developing the habit of writing regularly, something which many people lack the discipline to do on their own.
A journalism degree may be particularly useful if you are writing nonfiction. Some people also study English literature, which is helpful in that it forces you to read a lot of good books. (Of course, you can do this on your own.)
In fact, there is a certain danger that your writing career can be held back if you spend too much time in academia and not enough time writing. Academia makes you spend long hours reading and writing what you need to for courses, which is not always what you are passionate about reading and writing. In addition, many people take these programs during the most creative years of their lives, when (if you have real talent as a writer) you might be
better off working at a unionized job and writing in your spare time.
Of course, if your spouse has a good job and your children are old enough that you can take the time, an MFA might be a good choice (see above).
For a young adult, there is also the financial issue. School can saddle you with debts that a writing career will make hard to pay off.
However, I can safely say that the vast majority of writers do not have MFA degrees. Most writers are self-taught. They are people who discover, usually at a young age, that they like writing stories, so they keep doing it.
Later on, they may improve their skills by supplementing their writing practice with some courses or workshops. They may join a critique group or attend writing conferences, or simply read a lot of writers' blogs to get more tips.
Also (and sadly), having an MFA degree does not guarantee you will sell a manuscript. It might show a potential publisher or agent that you are serious about having a career as a writer and have taken the time to study your craft. But it doesn't actually prove you can write something people want to read. Nor does it prove that your book deserves to be published any more than the 100s of other manuscripts stacked up in the publisher's office.
The only thing that really counts is having a good book that matches what the publishers are looking for at the time you approach them. (And perhaps enough audacity to keep approaching agents and publishers until your book sells.)