the growth of the aro varies on many reasons like tank size, water parameters, diet, etc. if given the proper care i would say it would grow on a rate of an inch per month then after a year it's growth will start to slow down.
how big is ur tank?
if u keep in 4 ft tank...
with 3 times feeding a day.. it grow pretty fast.. but pls watch out ur feed as u dun overfeed and water condition..
had mine for 9 months now,and it was only 4" when i get it,now it is aprox. 10". And the first 7 months i feeed him with shrimps an hav now started fedding him with fish fillet ,and its still grown fast