My dad refuses to stop working at breakneck pace, which is affecting his health, his business (taking jobs and losing money), and our family.

I suggest having a consult for examinations by a neurologist - for brain disease related issues - and a psychiatrist - for mental health related issues. He may have problems related to either type of problem or both. In any case, he probably needs treatment to help with his symptoms.

Not totally sure how he's losing money and would rather not speculate. More information is needed.

Here's the thing, not all dementia is untreatable. It is symptoms of something else. Being depressed could be some type of deficit in his body, creating dementia symptoms. Your family should insist, even if you have to do a family intervention, that he gets a full physical to help him with whatever is going on.

Do the research and find a good doctor that has experience with these symptoms and schedule an appointment before the family encircles him, and for everyone to encourage him to find out what is going on with his health. He is scared, his actions prove that, some men think that they can push through whatever is going on, he is apparently one of them.

I do recommend that the family approaches this about his wellbeing and not business, it has to be about love for him or he will not be receptive, he is used to being the boss, let him have that and use dad, husband and grandpa as your motivation.

Best of luck getting to the bottom of this and may it be something treatable.

Have him tested for bvFTD, it effects actions and behavior, not memory in the beginning. Most people pass the tests for dementia that have it and are told they are depressed. Talked over money until you get an answer or he will blow it all an have nothing left to take care of him when he needs it. Go to a University hospital that specializes in behavior vareint frontal temperol dementia. bvFTD

Does your father have jobs in the sense that he bids on or agrees to provide a service, but rushes into it without calculating the costs involved so he doesn't ask for enough money to make a profit?

Not sure what "can't make the jobs work" means . . . Does your dad have grandiose plans and schemes which often do not work out? Common if there are some Manic-Depressive or Attention Deficit problems. He may also be working frantically to deny that he is getting older or "prove" that his memory and energy are not fading.

Is it a family business or his own? It sounds like you think he's making decisions differently than he has in the past- for example, accepting jobs or setting completion dates that he can't realistically fulfill.

Cognitive decline happens to most of us. Not dementia- just a general decline in our ability to make decisions the way we used to. The insidious thing is that we don't recognize it. It's a really good idea to have someone working alongside you who knows how you used to make decisions to give you feedback.

If it is a family business, then setting up some sort of committee to make decisions on accepting jobs might be helpful. If he is working on his own, can he hire a project manager who can influence the project's progress? I think instead of framing this as "you are working too much" you could frame it as "the jobs aren't working out the way you expect, are they? How can we get you some help with it?"

Depression definitely affects the ability to make decisions. He might just need more support in the business. Maybe you can convince him to try that.

Would it help to connect him to some business networks that can advise and mentor him for better business practices? The U.S. Small Business Administration has free mentoring from SCORE mentors, free online workshops, etc. This is the SBA website https://www.sba.gov. This is their learning center https://www.sba.gov/learning-center. Some people have no hobbies and can't imagine themselves not working. This is a very difficult business environment with coronavirus. Many businesses have had to close.

I'm a little lost on your question. You said he can't make jobs work yet you also mention it is affecting his business? Does he have a business and also work at other jobs?

I don’t see how you can force him to speak to anyone. Do you have permission from him to speak to his doctor? Perhaps start there and see where it goes.

All the best to you and your family.

The idea of success to a man is defined by what he has accomplished. You can't just tell a man who thinks that way to stop working.

Perhaps he needs something better to do with his time, however. When my dad retired after a 35-year professional career, he was more than ready to do it, but he also needed something to do. He got extremely involved in his community.

If your dad has done enough to support the family as I'm sure he feels was his duty, then perhaps he can be guided into volunteer opportunities that will help him by being both gratifying to him and raising his spirits through socialization.

Sometimes doing for others brings greater rewards than the best-paying job, and it certainly would do so if he's continually having difficulties at work.

Teddy Roosevelt talked at length and often about how hard and how fast and how ongoing he ran, and said that depression cannot catch someone who runs fast enough. He never stopped. Type A to a fault, with a fragile childhood, out of which he became a contender in almost everything. A shot in the chest didn't even stop him. So Dad's got some good company.
And to me it sounds as though your Dad is indeed running as fast as he can. When we are older and continue this it creates anxiety that can "look" like confusion and dementia. Trust the test. For now he has NO diagnosis of dementia and I would leave that alone.
Now, as to intervention. No. He isn't an alcoholic or an addict or a child in need of mental help. He is a person who is likely a type A and likely always was. But a family meeting? That is great if you all meet first and decide how it will go. It needs to be gentle and loving. It need to be "Dad, likely there is no reason to worry, but we worry for you. We don't want to lose you. We know you thrive on the activity, but we are worried". Then let HIM talk. If he wants to.
Men are alway Mr. Fix its. It is so hard for them when things don't have a clear answer and a real path forward. They don't like to discuss and worry things often enough. They want to act and fix things, and when that doesn't work they are nervous.
You say your Dad has been diagnosed with depression. Was medication tried for a trial? Did he not want to try it. Or did he try it and not have it work?
How old is your Dad?
My final thing, after you lovingly and gently talk to him is to tell him that you are there for him, will be his rock and support, that you love him and admire him, and will do anything you can to help. Then, quite honestly, let him alone unless there are new things that scare you a lot.
I think its wonderful that you love him enough to try.

Unless he sees there’s a problem and wants help with it, getting a professional involved won’t do any good.

Has he worked most of life? Mine has. He’s pushing 80 now but has worked since he was 8 years old. He has to be busy! He just doesn’t know any other way. If he retired it would kill him.