Someone is a 5% owner and has passed the age of 70.5?

Is that a question, or a statement?

A question. I was simply adding details to the question.

How do you calculate a required minimum distribution if someone is a 5% owner and has passed the age of 70.5?

You start by looking at the plan document because the plan can require distributions in amounts greater than required by law. You also need to make sure you comply with the timing specified by the plan.

I guess we're all wondering what we're missing.... you calculate it just like you would for anyone else, only the 5% owner does not have the option to postpone even if still an active employee.

DC plan or DB plan?

DC plan

as a general rule you take the ending balance as of the prior year and divide by the appropriate factor from the uniform table:
age factor
70 27.4
71 26.5
72 25.6
73 24.7
74 23.8
75 22.9
76 22.0
77 21.2
78 20.3
79 19.5
80 18.7
81 17.9
of course, nothing is ever that simple. sometimes there are possible adjustments that would have to be made to the account balance - though I dont think that often.
if the 70 year old had a young (more than 10 years difference) wife then its possible that using the joint table might be desired....oh, oops, not politically correct, I suppose the 70 year old lady could have a 50 year old muscle bound macho husband....