I think it is older than that, but you are right, usually giant breeds (especially Great Danes) liver shorter lives. Although, my sister and her husband have a Dane and I think she is 9 now.
Sadly our Landseer had aplastic anaemia or myeloid leukemia - only one way to check for this, and it it by taking a sample from the hip. A painful procedure which will cause discomfort for a couple of weeks afterwards. So I asked the vet what he would do if it was his dog, and he said nothing. So we decided to let her enjoy the rest of her life without meddling with her, as she was pain free at that point. So she was nine years of age, and I did feel cheated, as I hoped she would be with us for longer.