I'm a middle aged man with a hemoglobin over 18 and no one seems to be concerned

High/elevated hemoglobin levels are definitely a health concern, as they can indicate heart, lung, and kidney disease. For adult males, 18 is just on the upper end of the normal spectrum. You say your levels are over 18, but what are they? 

In any case, if your doctor is not concerned, there might be a reason for that. Have you had a thorough medical that turned up nothing else? Are you a smoker? (In that case quitting will help your hemoglobin return to normal and nothing else will, as your body is trying to make up for the lost oxygen.) Of course, you can always seek a second opinion if you feel the need.