I feel worthless - like i've never achieved anything and never will

Could be worst. You could have herpes.

You're young enough that you're not yet an irredeemable failure.

What? Your in your teens im pretty sure its normal to not have accomplished much if anything in such a short amount of time...
Why not set some goals and start working towards them. This might help you feel more accomplished

It's normal for me.. I feel that way too.

We all have came to that stage in our lives. Life can be tough, but my mom and dad always tell me when the tough get's going you got to get tough also. Just because you didn't get it or you may not be where you wanna be you can't throw in the towel just because of one mistake or a couple you loose when you say you can't at life.. . People will always down you.But you have to realize that it's not them in your position and there words are nothing to you. Look at yourself every morning and say to yourself.. .Today i will not give up.. And try your best and if your best wasn't good enough... . Make those blue prints and hit it again. Prove it to yourself that you can. Forget The Pressure

Doogie Houser was a Doctor when he was your age, you should be ashamed.

Obviously you have achieved something no other human has ever achieved before; you know the future. At your age to say you will never achieve anything is just stupid. The fact that you haven't achieved anything in 16 years is also pretty lame as you still a child; what exactly did you expect to achieve before you are even an adult?
Why don't you enjoy your childhood and wait a few years to stress out over things like your achievements.