We have a very handsome black Great Dane who will be six years old this January.
Very good health fantastic family dog.
We are interested in studding him out to get pick of litter, how do we do this?

Kind regards
Linda & Calvin

I would think at 6 years old its maybe a little too late, to be used at stud for the first time.  My advice to you is go back to your breeder, and ask their advice.