if i go to tafe for 12moths then apply for uni. will i be with the year under me

Haha, I see that you are from Australia, so I don't think that many people will understand what you are talking about. Luckily, I do. Yes, I believe that you will be with students under you, but remember, age doesn't matter. There will be people older than you in your class too, that wants to take the same course as you even though they are already later in life than you. Does it matter? You can still make friends, and hopefully you will find people in your age group as well. Everyone from all ages go to university, so I don't think it is something to be worried about. And that is why you don't fail HSC. Hopefully I won't. :)