Buying new boat

As in you'll just get to big, and probably bored and they're not the worlds fastest boats. 

If you’re predominately sailing by yourself then the Feva was a rubbish suggestion to begin with.

I would suggest that you go for something along the lines of the Byte C2. Its light has a nice rig. Much better than a Laser IMO. You’ll get a good few years out of it. Maybe a Blaze?

It depends what you are looking for, but generally I would go for a boat that people your age sail at your club.  Also you have to consider how often you will sail with you sister.

If you are going to sail on a regular basis with your sister and she is smaller than you, then the Feva XL would be a good boat to get going in.  The Feva also has good sized fleets, lots of people your age racing them and lots of training.  However, if she is the same size or bigger than you, the Feva XL will be too small.

If your sister isn't going to sail with you that much, I really wouldn't get the Feva.  Given your age, if your anything like my brother, you will grow out of the Topper in a year or so.  However, its a great little boat, great training and racing etc.  If your sister is small, if would be just big enough to occasionally sail with two.  The laser radial is another boat I would look at.  Its not the nicest boat to sail, nor would it be suitable for two people. Its a simple boat to sail, but very difficult to sail well, if that makes sense. 

The byte, well I am going to basised, as I do sail one.  Anyway, its a great boat.  The fleets aren't huge.  Due to the layout it is possible to sail with two. 

Only problem with a Pico is the lack of a decent circuit (at least in comparison to the Laser). 

I would get a standard laser. 

You have the option of 3 rigs as you grow up / lack of wind  

There is a good circuit so plenty of people to race against

It is possible to sail 2 up if you want a laugh.

On the odd occasion you do wish to sail 2 up, you could always borrow a club boat