Unless the tank in the 150 was empty when you added that old gas then the old gas is not likely to be the problem.
There is no way of making much of a guess as to what the real cause is because what is missing, spark, fuel, or a combination of the two (they’re related), is unknown.
Spray some aerosol carburetor cleaner into the intake and attempt a start. If it runs for a few seconds then it’s a lack of fuel problem. The lack of fuel could be related to the pump or its controls and this is where the diagnostics start.
Making a sheer WAG out of the blue I might take a stab at a bad fuel pressure sensor or the control circuit for that sensor.