What size do tapejo and steindacheri max out at ?
Used to breed Tapajos, ime they typically get between 6 and 7 inches, occasionally a bit larger. They
can get 8 inches, but most people will see closer to 6 or between 6-7.
Altifrons can be 10"?

I thought max size in the wild barely hit 9 inches,
Two things about wild size-- 1) may depend on location and wild environment and 2) some fish grow larger in a tank for various reasons, including feeding.
Not everyone will get the same total size or same rate of growth for a species, depends on several factors, like tank size, water characteristics and what you're feeding. I keep seeing some people say this or that species is slow growing when for me they're not slow growing. A lot goes into it, which might include the genetics of the individuals you have, stock levels in your tank, temperature, water changes, dissolved oxygen levels, etc. Last but not least, the ingredients in your food and levels of protein, which is not always a matter of more is better.
Source of protein can matter-- total protein listed for a food can come from various ingredients, including junk ingredients in some foods that mostly turn into waste.
Levels of protein matter, more is not always better-- they do a lot of studies on this kind of thing and there's always an optimal range for protein levels, lower or
higher and fish grow slower.
I have them in my community tank and they are barely break 6 inches but I have them little over a year.
Most cichlids are not done growing after the first year. Ultimately, though, your results can vary due to some of the factors above.