I am also 17 and have this fear.. although this is no consillation, i have seen so many posts by 16,17,18 year olds with exactly the same fear.. I have been told that it is the 'realisation age' where you realise that life has an end.. im told that it gets easier with age if that helpss..!
I hate the thought of dying or being in pain, also the thought of watching my grandparents/parents go through it and knowing i can do absolutely nothing.. i guess we have to hold on to the fact that it is a natrual part of life that cant be changed, everyone goes through it the same as birth! are you religous at all?