Hi,
Make up your mind now. Consider this:
1-You like working on abstract concepts? Then go for Electrical/Electronics/Computer Science etc
2-You like working around technical drawings, big machines? Then go for Chemical/Mechanical
3-If you want to work with buildings, static structures, then go with Civil Engineering.
There are only 4 Main Engineering fields, called the mother engineering fields, and all the rest are derived from them. They are:
1-Mechanical, Civil, Electrical and Chemical.
So i suggest you pick one of the four above and then do your post grad in a specific field. There are not many career options in Aeronautics in Pakistan or in fact elsewhere in the world.
I know you are young, and must be like i love airplanes, i want to design them. Reality is, when you graduate and get a job, you'll realize you cannot even design a simple bolt on your own. You'll need to follow design rules, peer checks etc.
Hope that helps.
BTW, i am Electrical/Electronics Engineer.....and by the time i was in grade 6, i knew what i wanted to study. It's not always fun, but you have to deal with it.