I'm fond of paraphrasing this (badly) but it's about time I stop mangling the master's words and let him speak for himself. If you've asked how long it takes to get good at drawing, here's the simple answer.
“From the age of 6 I had a mania for drawing the shapes of things.
was 50 I had published a universe of designs.
But all I have done
before the the age of 70 is not worth bothering with.
At 75 I'll have
learned something of the pattern of nature, of animals, of plants, of
trees, birds, fish and insects.
When I am 80 you will see real progress.
At 90 I shall have cut my way deeply into the mystery of life itself.
At 100, I shall be a marvelous artist.
At 110, everything I create; a
dot, a line, will jump to life as never before.
To all of you who are
going to live as long as I do, I promise to keep my word. I am writing
this in my old age. I used to call myself Hokusai, but today I sign my
self 'The Old Man Mad About Drawing.”
― Hokusai Katsushika
Got 5 minutes? Treat yourself to this delightful little documentary: