From my experience, given right conditions, a 1 incher can get to 6-8 inches in 2 years. Then it slows down somewhat, say an inch per year.
It can depend on the fish though, I had a 8 inch it grow to 12 inch in 2 years. This one just had a massive growth spurt after 8 inch mark...... The point at which the growth in general should slow down....
After 8 inch, you notice less length , but more bulk and depth growth.