The only way it would be considered a problem is if you are focused on masturbation to the exclusion and detriment of other activities you enjoy. If you find your thoughts are constantly focused on masturbating, or when you can next find some alone time to masturbate, while you are doing other things you enjoy, then it may be an addiction problem.
I guess people 'can' get addicted to masturbation especially if they use things like porn as part of it. Something may be categorized as an addiction if it takes the place of emotion or is a way to avoid something. Example, you feel sad, you masturbate. You feel angry, you masturbate. You avoid feeling the emotion through the activity. Otherwise, you know, what is the harm? Is there a wife complaining you don't have anything left for her or something?