The difference in flight time can also be in the way two individuals fly. If one is running flat out most of the time and another is generally cruising and only throttling up for climbs and manuevers, the one who is using less throttle for the majority of the flight is going to use less fuel per minute and thereby experience longer overall flights with the same amount of fuel.

In my experience I've noticed that my warbirds run out of fuel relatively quickly from maiden through the first 8-10 times out. After that the flight times increase substantially and max out after about the 15-20th flight. I know it's a factor of throttle use since the engines are always proven and well broken in and the fuel type stays the same. It's a matter of my keeping the speed way up while I'm getting comfortable with the plane and determining it's personality, once we get well aquainted fuel consumption eases up since I'm not keeping it wide open, or close to, for most of the flight. In some cases my flight time can more than double as half throttle is discovered to be plenty for level flight once the powercurve and energy needs for a particular airframe are learned and aerobatic throttle management get smoother as the "tinglies" wear off with the new plane.

Those newer to the hobby tend to show the same type habits, keeping a lot of juice on. As your skill set develops and you become more comfortable with flying, your throttle management will get better and yield longer flight times. Two areas where a lot of fuel is consumed unneccesarily is being "late" backing off the gas coming out of the backside of a loop, and "jack-rabbit" accelerations as opposed to smooth power increases. Both of these can really gobble up the fuel.

If all of your settings and set-ups check out then I would suspect that this is your case. Even if you find a set-up issue in this case, I think that over time you'll notice that there seems to be more fuel in the tank than you expected at the end of your flights and you'll begin to stay aloft a bit longer and longer.

Welcome to the hobby, happy flying