A lot of claims of three foot plus silver and black aros, yet you really don't see many people posting proof of such. For the most part, I haven't seen many people posting silvers over 30" or blacks over 24".
As for mine, my two silvers are 5.5-6 years old and 29-30". They grew rather quickly up to 24-25" and then the grow has slowed drastically since.
My two blacks, one is 26-27" and going on 5 years old, was a slow grower but not a very aggressive feeder. My youngest black is 25-26" and only 21 months old.