I have the same experience. I'm 45 now, still can't visualize in my mind (and I have weak dream recall). I think there are categories here. Some people are really gifted and can visualize anything on-demand and interact with those visualizations in very interesting ways. That blows my mind, seriously. My wife is like this. Other people exist in a gradient between people like us with no visualization and the people who have absolute control. Those people can sort of acquire and train the skill and over time will improve, mostly organically, too, I think. Those people will tell people like us that we are not trying hard enough. If only we would tried harder, we, too, could acquire and develop this skill. But as you know, people like us cannot simply acquire or develop this skill. We are missing some prerequisite.