Denial- for sure. Feelings of invulnerability- absolutely. But practicing when the stakes are low (i.e. kid is in middle school, so parent is driving, nagging, is the backstop every time you leave the house) is a good way to train the muscles to take over by HS. I know a college kid with CF; boy, is that disease time-intensive to manage. His parents started transitioning responsibility for the regular stuff early; he was clearly ready to move away for college although I’m sure their hearts were in their mouths.
OP- what does your son want? To move out after he graduates from college? Then let him know (lovingly) that he’s got a couple of months to prove to you that he is fully in control of his own care. And that showing you that he’s stepped up is the next step.