I commend you for coming forward with this issue, I am sure it hasn’t been easy for you to talk about it. I think the question you might need to ask yourself is why exactly you feel you would like to be castrated per se. Do you simply feel that having a high sex drive is a nuisance? I feel that I need to reassure you fully that it is entirely normal for you to think about sex a great deal at your age and for the drive to be exceptionally strong. There was this great scene from Buffy the Vampire slayer where Cordelia and Xander are sneaking around some sort of warehouse full of weapons and Cordelia asks Xander: “Do guns make you want to have sex?” and Xander answers: “I’m 17: linoleum makes me wanna have sex”. There is no ‘normal’ amount of masturbation or sex. Sexuality is a normal part of life just as eating drinking and sleeping are, and should not be a source of pain or disturbance.
I am wondering if there is something deeper that might be bothering you. Do you feel comfortable about the things you fantasize about when you masturbate? Does the sex bring about painful memories? If you are having sex with partners, are you truly attracted to the people you are having sex with and are you having sex with them for reasons that feel right? Were your first sexual experiences negative? Have you been raised in an environment which has made you feel guilty for having certain desires? Masturbation can only hurt you if you feel bad about it. As far as I know, no surgeon will perform a castration without having documentation from a therapist testifying that there has been some kind of psychological evaluation. This type of surgery is a one way road, and you are still very young.
Before you look into surgery, I strongly recommend you start by contacting a psychologist or sexologist, as they might be able to guide you further.
Good luck, don’t hesitate to write again if we can help you further,