My advice is to get some A levels and do a degree course that will open a lot of doors should you wish to do something more financilly rewarding than making guitars - electrical engineering or whatever.
Do the guitars as a sideline
If you pursue it you will probably end up self employed- so the certificate won't mean so much as the practical experience.
You can teach yourself with videos and books in your own time anyway.
I kind of learnt most of my stuff that way, and I still pick peoples brains for info even now. (Tim will vouch for that)
This forum amongst others is helpful too....
But you must practise what you learn to make it all real and develop your skills