I was about 21/22 when I realised my parents were people!! And come with all the infallibility's of 'people'. Just because they have an opinion on something, doesn't make them right. I love my parents a lot, and they're fantastic people, but they don't have all the answers and they may be right on a lot of things, but certainly not on everything. And even the fact that I can say they're right on a lot of things, makes them exceptional.
Going against your parents, doesn't make you wrong, or mean you love or trust them any less, and maybe they need to be told that. You have one chance at your life, and you have to live it the way you see fit. If your parents have done their 'job' you will have a good, fair view on the world, and they have to trust you now to live your life the right way - being the way that you want to live it.
I'm not exactly 'old' i'm 30, but if I had the last 15 years over, the only thing I would change is my self confidence. the older I get, the more I feel comfortable in my own skin. What other people think really doesn't matter. They have their lives, and you have yours. I know, more than i can explain, that that is easier said than done.
But sweety, you haven't hurt anyone, you haven't stolen anything, is wearing your chain really going to affect anyone elses life? Sometimes it's parents that need to be taught. x