Cut fingertip: What should I do?

Over a decade ago, a guy lost the very tip of his left index finger—about an inch or so longer than a fingernail, really—after his hand got caught in some machinery propeller. He’s 60 now, works a blue-collar job, and honestly, he’s in better shape than most people half his age. He's pretty much a powerhouse.
Fast forward through all those years, and suddenly the finger is swelling up and turning a noticeable shade of red every single day, accompanied by this dull, nagging pain.

Does anyone have any idea what might be going on here? We're all overreacting and panicking, while he’s just sitting there acting like it's nothing. :-(

It’s obvious he’s got an infection or something starting up, and he needs to get to a doctor immediately. If he just sits around waiting, things are going to get messy fast—he could end up losing a finger, his hand, or who knows what else. 🤷