Gearing seems decent... at 90 rpm you should be doing 20 mph.

My 90 rpm on my road fixed gets me 22 mph since I run a slightly taller gearing.

Guessing your friends are pushing a slightly taller gear and don't have to spin like gerbils on crack to match your speed and if they have more miles behind them are in better shape and can sustain higher speeds for longer.

Or they are running geared bikes and then you don't have a chance to keep up.