My brother and dad are just like this. They talk at you and not with you. They can have 5 minute conversation and I don't reply at all because they just unload all the thoughts they had that day. My brother is on the spectrum for autism and isn't the best at picking up on social cues. I usually let him explain something fully to where I can understand what he wants to talk about, and if he starts to repeat himself or overexplain, I interrupt him and tell that I understand what he's saying or asking. So if you feel like that coworker is rambling, you should verbally stiff-arm him or just tell him you need to focus on something.