How to deal with a deep-rooted feeling of apathy?

My mind is way annoying to listen to and I don’t like it!

I'm 45 years old and I have a hard time coming to term with the fact that the majority of my life---the one which supposedly should had been my golden years---lies in the past. I know I'm still alive but I just can't drum up much enthutiasm for an existence which I mostly see as sad leftovers of something which wasn't worth much either. I simply don't care much. I can distract myself for some time, but I have this deep feeling that, well, what's the point.

And I can ignore it, for some time. But ignorence can only go so far. At some point you need some hope, some sliver of meaning and purpose. And I just don't see it.

And this is all awful impractical, because whenever I try to strive for anything, my brain just goes, “narh, why bother struggle when it doesn’t lead to anything”

Is there any clever way to turn stuff like this around? Some NLP stuff to nudge me towards a less self-defeating mindset?