If you are choosing your GCSEs, it is important you start thinking about Science subjects and other areas linked to engineering, such as Design and Technology. You may also find that your school offers GCSE Engineering or the Engineering Diploma.
If your school offers separate science GCSE subjects, ensure you take Physics as one of your options. This is because if you want to go down the degree route to aerospace engineering (particularly if you want to design aircraft), Physics A Level is a must. Chemistry and Biology can relate to certain aspects of aerospace, such as fuel systems but Physics is very important.
If your school offers double Science only, you need to ensure you take Additional Science as well as Core (21st Century) Science. In Additional Science you will cover Physics, Chemistry and Maths in more detail which again will enable you to take A Levels in science subjects.
Other useful subjects include: Languages (aerospace is a truly international industry!); Geography and Business Studies.
Of course, equally important is Maths and English and you should aim to reach grade C or above minimum. Most apprenticeships, colleges and universities will expect you to have 5 GCSEs minimum grades A*-C with these two subjects included.