You should get at least some credit for the tafe course you do (as long as it relates to the degree you choose at uni).
You can either finish your course at Tafe and re apply to uni as a 'mature age' student at 21, hoping to get credit for your tafe course...
Or...
You can Take up subjects through 'unitrack' (i think thats the name) where you pay
upfront for individual units at uni (that you should pick from the course you want to do, then it gets used for your degree) and I think you have to get an above credit average and you can apply for a degree.
Don't quote me on this, its just a rough idea of what you can do if you don't want to wait till your 21, and the only problem is you have to pay upfront for the units (can be costly but its the same as HECS you just pay it now), I know if you ring the uws hotline they will explain it all further and I'm sure theres a 'pathways' site on
www.uws.edu.au that explains alternate paths to uni.
Goodluck,
oh and ignore people who got 99.9999 as their uai
if they're being mean...