Yeah 2-3 years to get to that size but the age will really be guess work i know that fish with large,thick scales will have some age on them. Then body thickness in general like girth it takes them some time to get real heavy. My 6 year old 13" male rd wieghs twice as much as his son of 3 years who is only a inch shorter i have never truley wieghed them but just feeling them when in the net is a huge difference.
how long do they live? do you think he would still be a breeding candidate since he is over 12"? is there a specific age range when they stop being interested in breeding? or are they like energizer batteries?