Let me preface what I'm about to say by letting you know that before I retired, I worked as a psychologist and was a Certified Sexual Addiction Therapist (C.S.A.T.), so I've worked with a lot of sex addicts over the years. If you scored an 8 on the S.A.S.T., you are definitely NOT a sex addict, at least not at this time. Generally, you need to score 11 or higher on this test before you can be said to have a sexual addiction. However, a score of 8 for a 14-year-old is a bit irregular, and I'm worried that you may be setting yourself up for a sexual addiction somewhere down the road.
You might want to read a book titled, "Out of the Shadows: Understanding Sexual Addiction", by Patrick J. Carnes, Ph.D. This is a basic text on sexual addiction, and it will give you some of the background you see in sex addicts, as well as tell you some of the warning signs to watch for. This is probably the best book out there for outlining the basics of this disease.
You might also want to take a look at a couple of websites:
Society for the Advancement of Sexual Health
Both of these sites contain lots of information about sexual addiction and recovery, including information on the various Twelve Step groups (similar to Alcoholics Anonymous) which exist for sex addicts. (Sexaholics Anonymous, Sex Addicts Anonymous, Sex and Love Addicts Anonymous, and Sexual Compulsives Anonymous). Although you can't attend an "in-person" meeting until you are at least 18-years-old, you can join a telephone group or an online meeting, and information on both of these kinds of groups can be found on the websites. And you can also find information about the Certified Sexual Addiction Therapists here if you feel it might be beneficial to talk with someone.
Now while what you are doing is normal for a 14-year-old young man (watching pornography and masturbating), you might want to limit how often you engage in such behaviors. As an additional source of help for you, consider joining one of the online support communities. I can recommend two such organizations:
Both communities have support groups for sexual addiction, and they might be able to help you curb your desire to watch porn and masturbate.