It's difficult to defeat the overwhelming feeling of "There is no future (Or at least not a good one), so what's the point?". I feel like even if I live to 100 we're not going to be anywhere close to a Star Trek utopia, but more smack dab in the middle of a Dark Age.
What to do when you're still gonna live. Plan for the future as best you can I guess. Try to be healthy, you don't want to be 70 in poor health in the Dark Age right. Try to save money for as long as money is worth something, better to have it and not need it than the reverse.
The feeling you're talking about can be partially treated by taking action. Even the small more pointless action like recycling, composting, going vegan - never mind the bigger harder stuff.
The future is worth fighting for, at least I think so, but it isn't an easy fight by any means for sure.