i.e. you are exactly like every other 16 year old I ever knew.
Most of them because more motivated once they started university and were able to focus on what they enjoyed studying. I'd be more worried if you were motivated at 16, because then you'd probably burn out, or grow up to be an obnoxious brain box.
Also, since you sound like you are in the UK, you should realise that grades don't matter here. No-one will ever ask what you scored in your maths A-level. Your success in life will mostly be determined by the connections your parents have. The only thing you can do to improve your chances is network and make some more connections of your own at university. Plenty of top jobs go to those who graduated with the "gentleman's third" because they spent their time networking rather than studying.