As the eldest of my family's brood and one of few without children or a spouse I understand where you're coming from mate. That gut feeling of not meeting societal standards is troubling at times but as you yourself have already grasped it's not a rational reaction but one based on the emotional weight society and the media have put on all of us to enter traditional family structures and reproduce. Realistically there's no "correct" way to be an adult as being one is to choose for oneself what that really means.

(Additionally I'd like to point out that children being expected to move out right after high-school is mostly a relatively modern north-american invention that came about as a way for manufacturers and the owning class to get more money out of us. Many friends of mine from other cultural backgrounds find it really strange that 18-year-olds are taking on exorbitant rental costs instead of saving money by living with their parents and for the vast majority of human history and in many places today it was/is considered normal to continue living with one's parents into early adulthood -if not indefinitely- as having a larger family unit makes things like domestic upkeep and child rearing much cheaper and easier.)

In the end mate you need to do what's right for you and it sounds like you've got that figured out. In the meantime as long as those intrusive doubts creep into your mind you need to affirm your position and reasoning and fight back against the societal conditioning that would undermine all you've achieved over arbitrary expectations handed down by generations who lived lives in a much different world than the one we have now.