Anyway, Puggy was right... a Starboard Start or Starboard Go or similar. They are about 200litres and have a centreboard... that is like a keel on a yacht...... and it is in addition to a normal fin at the back. A 200L board is big enough for fat old people to learn on, but about 120L will float you very well if you are an average 14 y/o.
The only advantage to the big boards (at your weight) is the centreboard stops you from drifting sideways too much when you are starting to get going.

Therefore I recommend IF you are dedicated and really want to learn, (1) read a how to learn article, there are plenty on the web. So you can get your head around what to do
(2) get one lesson (about $50-80 I think)... not the whole learning course or 3 (?) lessons.
(3) After 2 hrs or so lesson you get about a 130L freeride board, no more than 5 years old. At 130L volume you want the widest board ... it will be about 66 - 70cm wide. Don't get a 130L that si any narrower than 66, it will be too tippy. Ask some local windsurfers to explain to you what to look for like soft spots, if it too heavy (water in it) and so on when you do find one. DON'T ask a guy who is selling one cos his will be perfect of course.
(4) you'll need about a 4.0m sail to learn on and probably about a 5.0m for after a few sessions. Don't buy a 10m sail just cos ur bro' has a 10m kite!!!!

Keep asking here we'll get you hooked up.... and hooked too prolly

i weigh 48kg

Hey Kitesurfin,
My son just started this year. He's about yor age and weight. First up he was on a 220 litre Windrush (20 year old longboard) with a 3.2m Aerotech trainer. He had about 4 to 5 sessions on this board getting blown downwind but still out there having fun. After he could tack and uphaul this, I put him onto a 140 litre freeride board at 68 cm wide with a 4.7m NP Combat ('99 but as new condition). Once again, about 5 sessions on this and he was playing with the harness, beach starting and sometimes using a 6m on those 5 to 10 days. We've had some good wind here recently so I put him on a 103 litre free ride (F2 Ride 277 65 wide) with the 4.7. He has had some really good planing runs in the straps and harness so the bug has truly bitten now. Now he is working on waterstarts. Even though the Go boards and similar are really good to learn on, you can start out on on some older gear while you learn what it is you want to do. Maybe a lesson and hire would be a good way to start! The best thing you can get first up is a life jacket. I know none of the good guys you see are wearing one but when you start out you can get really tired easily so it is good for just lying back and having a rest! Plus it'll get your Mum off your case!! If you were over here, we could lend you some stuff to have a go! I bet the W.A Guys could round up a basic kit for you to have a go on!