You can look through my old thread here.
http://www.monsterfishkeepers.com/forums/showthread.php?t=189144
I know he was 3" when I got him because I measured and I know he was 20" when he died, because I measured. I had no desire to take a picture of my dead RTC against the ruler. You can see him at 18-19" in the last pic in the photo thread those were the final photos I took. He would have been even bigger to but survived through a 3 day power outage where the water temp dropped to the mid 50's and he didn't eat for a bit after that, that was around the 1' mark.
If you don't take my word for it's fine, but if you look through my posts you'll see I am a grown adult who posts true factual information.
-Oh and I brought up what I thought was fast growth to BassLover in a previous thread from months back and he said it was completely normal. Which leads me to believe either many people have really slow growing fish or they are doing something wrong. (IE; not enough food, not enough water changes, not enough space to grow etc)