Right around a year to 14 may be 15 months for some and they are jet shinny black. They are pretty close to done growing at three years, they will still grow some after that but it is very slow. This all assumes a good steady feeding schedule during the young years of course.
I honestly love them and have to agree with Don at SMR when he calls them a "cheap and legal version of Indigo Snakes for the common man".