I'm a 19-year-old college boy, and I masturbate 3-6 times a day for about 30 minutes apiece. Is this unhealthy?

I wouldn't say it's unhealthy, but you are certainly devoting a lot of time to masturbating – up to 3 hours per day. As long as masturbating isn't keeping you from doing more productive things, like studying, I'd say it's okay. But if your grades are suffering, consider cutting back. It's not that frequent masturbation is unhealthy, just that your masturbation habits shouldn't intrude on other areas of your life.