I am not a big expert on this, but I assume it will grow as fast as other Arowanas if under right conditions (water parameters, tank size, food variety, etc.). I have read where some have grown 3/4in every month for like the first year or something. I doubt it will grow any faster or slower than other silvers.
I think it depends on water parameters, feeding, and size of tank. My friend has a black aro and her's just is SLOW but my black aro seemed to explode in my tank!