I have to wonder - Did Bernie ever try specifically to win over older people? Did he ever make a big push for that? He did way better than I ever truly expected, but he losses among older voters was just too much. I don't think his democratic socialist label really helped in that regard. America has gotten more accepting of many things over time, but let's not get ahead of ourselves with that.
He constantly talks about the same stuff he campaigns on re: SS, Medicare, etc. in the Senate, so he did have a platform to attract older voters, but it's time consuming, and I'm not sure he had time for it. If I were him, I would've taken advantage of Fox News earlier. Fox is a very useful outlet to reach older Democratic voters, and neither Dem candidate tapped its potential.