If you read the posts here they all say the same thing.
You can be fired for any reason except a protected one (Age, race, Sex, etc.) or no reason at all.
You would need to prove that your father was fired because of his age and if the company has employees your fathers age then age discrimination would be hard to prove.
Bosses are allowed to be jerks and tell you to go home.
They do not have to tell you did something wrong and give you a chance to fix it.
You can get terminated because your name is Bob or because you wore blue shoes.
Employers do not have to give written warnings.
Your father needs to file for unemployment insurance asap and start looking for a new job. With his experience he should be able to get a better one - try another local dealer.
I would NOT go to the dealer on monday and confront his boss as this may land you in jail or could make it harder for your father to find a job. If he is upset then HE can always contact corporate / owners and let them know what went on. You love your father - just don't make things harder on him while he is looking for a job by getting in the middle of this.