- I've had lots of practice writing. I don't know if I've hit the 10,000-hour milestone yet, but the more I've written, the better my writing has become.
- I've read lots of books. This is a corollary to #1. Reading is one of the best ways to become a better writer IMHO, and by my conservative estimates, I've read more than 2,000 books so far in my life, not counting essays, papers, and other passages that were required for school. That's a lot of examples to draw from when it's time for me to write my own books.
- I've had more life experiences. A couple of years ago, I read some of the short stories I wrote when I was under twenty. Not only was my writing laughably awful, but the things I wrote about and my viewpoints were naive. Even if I had mastered a command of the English language at that age, my stories wouldn't be as textured as the ones I can write now, and that's due to having been alive for a few decades.
- I have more discipline. Having to juggle a full-time job, raising a family, and all of the other adult responsibilities in my life have taught me how to get things done. I don't always succeed in doing what I ought to, but I'm a lot better at it now than when I was twenty.
- Insomnia means more time to write or to think about writing. This is somewhat tongue-in-cheek, but as I get older, I've had more trouble sleeping. What do I often do when I'm lying in bed? I brainstorm ideas for my work in progress or new story ideas. If only my aging brain would hold on to more of those ideas until the morning when I can write them down, but that's another topic...
Richard Adams didn't publish his first novel, Watership Down, until he was 52, and Laura Ingalls Wilder didn't publish the Little House books until her 60s, so I still have many more productive writing years ahead of me. Chances are that I'll become an even better writer as I continue to age.