How do you part ways with a business partner and how old is too old to begin a start-up?

'My co-founder and I have built several companies together, but in the past year, it has become apparent we aren’t working well together on our latest venture. We’re short with each other, we’re frustrated and not seeing eye to eye. The worst part is we’re fighting often in front of the staff, and tensions in the office are high. We’ve floated the idea of working separately, but I think it’s better for us to go our own ways, at least for this project. 
How do I have this conversation with my co-founder? Right now he just feels like a massive asshole, but I know deep down he’s a good guy. How can we break up well? 

FROM: Breaking up is hard to do