How big do Albino Cory aeneus ( or whatever they are called today ) get???

I have a mob, ( 7 ), 2 older, and 5 younger… all adult sized now… or are they??? I just saw one of the older ones, next to the side of the tank, and it’s over 4 inches long… I didn’t think they got that big???

Normally 2-3 inches.
Tape a ruler on the glass at the same level as the gravel and see how big the fish are when they swim past it.

The females can max out at about 4 inches (total length, which measures the tail), or 3 inches (standard length, not counting the tail) , yes. People underestimate how large they can get, expecting them to stay smaller. But they're among several of the larger varieties common in the hobby.