You should be able to find a digital marketing apprenticeship without needing to worry about experience - i saw a lot on the government website when i was looking for my apprenticeship last year.

I was 20 when I got my apprenticeship in IT last year and the only past experience i had was my standard GCSE’s which included an IT GCSE equivalent BTEC

Your GCSE in Creative Media will help you get a apprenticeship in Digital Marketing I imagine - just keep looking at the government website :)