After boiling pasta and setting the water in which the pasta was boiled aside I noticed that after the water cooled it thickened. It sort of has the consistency of gravy. Would I be able to make gravy with this instead of using starch? 
I think you should read McGee on this one. Basically he says the 'water' from boiling pasta is very rich in flavor.  Italian recipes often suggest adding pasta water to adjust the consistency of a sauce, but this thick water is almost a sauce in itself. When I anointed a batch of spaghetti with olive oil and then tossed it with a couple of ladles-full, the oil dispersed into tiny droplets in the liquid, and the oily coating became an especially creamy one. Restaurant cooks prize thick pasta water. In “Heat,” his best-selling account of working in Mario Batali’s restaurant Babbo, Bill Buford describes how in the course of an evening, water in the pasta cooker goes from clear to cloudy to muddy, a stage that is “yucky-sounding but wonderful,” because the water “behaves like a sauce thickener, binding the elements and flavoring the pasta with the flavor of itself.”  