How do you recognize maneuverability? Length is in the specs.

You'll have to dig a bit as handling is hard to quantify but you can tell a lot by looking at the hull shape. Like I said in my other reply the profile of the hull tells a lot. A design with a lot of rocker will be very maneuverable for it's length. Look at the shape of the Frej:

Compare it to the Norton:

They're about the same length. It's no surprise that the Frej is much more agile.

Next read the description from the designer and any reviews. Stay away from anything that says things like "a bit stiff" or "good tracking." You want to read "responsive", "plenty of rocker", "very easy to handle" and "easy to turn." Designs for "surf" or "playing in waves" are very maneuverable kayaks.