Don't worry about this, I don't have a suitable reference in terms of the 5 year requirement and have been told this is fine! If you pass stage 4 you are told that references are still accepted if you haven't known them for 5 years (the example given by CTC is that those fresh out of uni will only have known their tutors for 3 years!).
Make sure it's not family and close friends though (although I sure you've noticed this stated on the online application).
edit: you started uni at 16??