Going to Uni doesn't mean you can't start up your own business, but it does mean you have a good back-up if your business does not work properly.
Going to Uni doesn't mean that you are unable to start up your own business; its just a 3 year (not that singificant) delay and you will probably be better equipped with the skills you get from many courses to start the courses.
3 Cambridge graduates started the smoothie craze by founding P&Js smoothies and made millions very recently for instance.
Plus, most people have the best social time of their lives at Uni.
Whilst it is perfectly reasnoble not to go to Uni, many people don't, if you have good grades and wouldn't mind too much studying something (might be management and relevant to your business) as well as enjoying yourself in socities and the independence youd gain, id say go to Uni. Not much you could do in terms of starting a business without any capital and at 17 anyway, noone would take you seroiusly... many people, like the cambridge grads that started P&Js, take a job for 3 or 4 years to gain some capital and then start their own business with the means to do it and will probably be taken more seriously as they aren't teens.