Wanting a tubal reversal

I'm 27, I have three kids of my own, My SO has one of his own. We've discussed wanting another together. He keeps telling me he wants to wait though, to be financially stable and such which I totally understand. I feel stable that we could and he's always buying expensive truck parts and playing with his money. I just feel like it's never going to happen and it's going to be too late in the game. How can I go about discussing this with him?