Just do it! And, it's important I think if one really wants to be a writer to do it regularly, preferably daily.
I've never really liked the word "can't" and fully believe that any of us can do whatever we choose. Only our own negative thoughts or self-talk (or mistakenly listening to others) stand in our way. Believe in yourself and do the work.
If we choose to be writers, we simply are! I first experienced this one day while working on book edits in a restaurant I frequented daily. Another fellow, who also happens to be a writer, whom I'd seen there several times, one day sat next to me and asked, "Are you a writer?"
It was the first time anyone had asked me the question, and I liked the answer that immediately came out of my mouth, "yes!"
I love, love hearing that someone wants to be a writer. As someone recently said to me, "it's our books, what we write, our writings that succeed us in posterity."