First of all, you can totally do it! The field is massive, but also full of very bad programmers, and seeing how you were able to write a coherent text of three paragraphs, that already puts you ahead of the curve. Determination and perseverance is key.
I would suggest to play to your strengths. Java is still Java. Most of the progress since the 1990s was in the libraries and tooling, which only recently have become passable. The language itself also evolved somewhat, but there’s nothing that you won’t pick up in a couple of days of working with it.
Start with [1], work through all the boxes that are unfamiliar to you, practice a little on a pet project, or an open source project, and you’ll land a job in no time.
Also, if you remember enjoying hacking, maybe pick that up again? There’s a massive shortage of security engineers at all times.