Every one consumes different volumes of air to each other when diving. I have seen open water students start a dive with 220 bar and return from an 18m 40min dive with 150 bar remaining in the cylinder. On the other end of the spectrum i have seen divers with over 1000 logged dives return from the same profile dive with only 10 - 20 bar of pressure remaining.
People tend to assume that if you are of a small build or even female that your level of air consumption would be of a lesser amount compared to being of a large build and male. Also it is the generally assumed that air consumption would be higher for a smoker compared to a non smoker.
From my experience the easiest way to try and determine which individual diver out of a group of divers will go through their air the quickest is to try and read the persons body language. ( or just talk to them)
Really it is simple, when a diver is nervous they will chew their air more quickly than if they were not.
It all starts prior to the dive. When setting up your equipment pay attention to how other divers are setting their gear up. Is the Cylinder place correctly on the BCD, are the regulators on the right?.
When some people are nervous they tend to talk excessively others simply go quiet and say nothing, try to read peoples body language or better still talk to people and ask how they are going.
Watching a diver try to deflate their BCD on the surface with their snorkel is almost a dead giveaway that the diver is unfamiliar with their equipment.
When underwater, things like poor buoyancy control or swimming with hands are good indicators that a diver will go through their air quickly.
When diving if you hear another diver making an Arrrgh type sound every time they exhale you can almost guarantee that they will go through their air extremely quickly,.
At the end of the day the easiest way to see who is chewing the most air is to look at the bubbles. More bubbles = More Air. :)