How do you deal with the thought of having to work for 40+ years and then when/if you retire, you're too old to do much?

I slack. Oh boy do I slack. I'd work so harder if I thought I would actually get something for it. In fact, when I started my latest job, I was doing just that, because it seemed this company was different, and it's something I'm naturally good at. Got commended by my boss about how much I was doing, how quickly I was learning, how in a year I had already surpassed the next most recent hire that had been there for 2 years... Then time came for my review, and it was a "meets expectations". Like wtf do I have to do to exceed expectations? Then not long after, they started denying me time off, saying I had taken too much. Supposedly we had unlimited PTO, of which I had taken 2 weeks so far that year (1 week in March, the rest just single days here and there), and my request was for a week in July... Anywho long story short, I've pretty much figured out exactly how much I have to fake being busy to not get negative attention, and I do that. I milk cases for all they're worth. And I'm still getting more done than half my colleagues. I hate it, but it pays decently, so I have a hard time throwing it away for something that might be more fulfilling, but doesn't pay as well...