Earlier quoted context omitted.
"Java (understanding the JVM and OOP concepts)" I am pretty sure that you can programm java without knowing details about the JVM and I would think, that most java programmers do exactly this. I think only in high performance scenarios knowing more is beneficial? But I have not touched java in a long time .. as I have indeed choosen the web as plattform. But I don't feel threatened by the high school kids coming from…
not feeling threatened doesn't mean you're not under threat. It's entirely possible that between your skill level and those boot campers is a few(dozen) percents of workforce. But at the same time it's entirely possible that if you are not as quickly progressing as the growth of the industry, you could become a part of the same percentile as bootcampers in no time.
Focus on what you can control and let go of that which you cannot.