Female sterilisation?

I am 18 years old and know that I don't ever want children. I haven't been to my doctor to ask him yet if I can have an operation to have my fallopian tubes severed as I suspect that he will say I cannot. Does anyone know what the laws are about this? (kindly refrain from telling me, 'Oh you are young and will change your mind because I won't. Anyone who tells me this will receive a blunt response as that is blatant ageism).