Second, most everyone is recommending other self-interested pursuits and I don't think you'll find the best fulfillment there.
For me, the answer to "what's the point?" is: kids. After I pursued all of my self-interested goals (resulting in a mix of failure and success depending on who's keeping score) I had kids and realized none of that stuff I pursued really, truly mattered. In fact I wish I'd had kids sooner, as young children (I've got three) are an especially thorough ass-kicking for a 40+-year-old.
Having kids with a like-minded, selfless partner is literally the very best thing I've ever done. And it's the best thing I suspect you'll ever do if it comes to pass. As a friend of mine (who also had kids later in life) says, you have kids and you realize "oooohhhh, this is the whole point".