What usually results from excessive masturbation in male adults and male teenagers?

Irritation. Other than irritation of the penis, not much, unless it becomes obcessive, which can be a psychological issue.
Losing out on life. This is a problem only in guys who get so obsessed with erotica that they lost time from studies, work, sports, fitness, romance, whatever else is important. Enjoying your body won't make you bald, stupid, infertile, short, hairy, smooth, or any of the other things you've been warned about. You stay comfortable, learn about your body and mind, and get prepared for adult roles.