a torn journal entry

How do I tell him that I feel like I am the one who made the mistake by thinking he could be mature enough to handle the responsibility of a relationship like ours? My life is full of required routine and expectations. I have responsibilities that I simply cannot put off ... I feel that he doesn't meet me on a level playing field -- he is smart, just not lived-experience full (if that makes sense). I should have known better. It is my own failing - that I don't value myself enough to date someone my own age. I feel like I am not good enough. I need to be single until I stop feeling that way. But how do I explain that without hurting him? It isn't a lack of love - it is a lack of connection. We don't fit. But he will take it personally :(