Further to my previous reply, picked up some leaflets showing that BA Engineering is again recruiting Apprentices to start in September 2015
As stated before there are two different Apprenticeship schemes
The traditional Aircraft Maintenance Apprenticeship and the Aircraft Appearance Apprenticeship [basically cabin work]
It does state grades A-C for for Aircraft Maintenance and A-D for Aircraft Appearance.
both state the schemes are ideally suited to 17-25 year olds [so being 20 should not be an obstacle]
Open for applications December 2014-February 2015
via:
www.ba.com/careers
Good luck with your search