I taught writing classes at the University of Pennsylvania for a number of years and I realized that all you can do is encourage people and give them assignments and hope they will write them.
In my early twenties, that's when I really began to write. Before that, I was too busy working, keeping myself going.
I don't know what makes a writer's voice. It's dozens of things. There are people who write who don't have it. They're tone-deaf, even though they're very fluent. It's an ability, like anything else, being a doctor or a veterinarian, or a musician.