I am 30, for the last 15 years I have always been thinking: What the hell do I suppose to do when I am in age of 45-50? I will be old at by that time, not heal

I am 30, for the last 15 years I have always been thinking: What the hell do I suppose to do when I am in age of 45-50? I will be old at by that time, not healthy, not smart and competent as I was in 20s. Obviously would be replaced by younger generations. And I will have a couple of kids too. I will raise them, work, earn money. All of my time will be devote to that. My days will likely pass meaninglessly. And in a couple of years I will be in retirement. And what do I suppose to do at the that time? The future sounds boring and scary as hell. I still think the same, and sometime thinking about it and it make me cannot fall asleep for about one hour. I don't want to live like that. However how do I want to live? I cannot answer it, I don't know.