Copywriting one of the few professions where a degree is not required.
That means anyone can become a copywriter, irrespective of their age, experience, background and educational history (or lack of it).
A background in English helps. You should also have an enquiring mind, store a lot of information and be able to make lateral connections.
Good copywriters are curious and don't wear blinders. Knowing how to write helps, of course.
But be sure of one thing: while the business of advertising can be fun, it's business, not art.
Ultimately, the clients pay the bills. The goal is to sell the clients' stuff. And, although there are many important things you know about advertising that your client might not, you'll never know as much about your clients' businesses as they do.
Part of your job is to draw that knowledge out of the client. And to distill that knowledge down to a key point that speaks directly to the needs of their prospects, catalyzing a message that's more than the sum of its parts.