http://new.britishcycling.org.uk/coaching/article/coast_awards_overview_page
Alternatively, Association of British Cycling Coaches.
BC do a CRB check as part of the qualification process.
You will need an up-to-date Emergency first aid Certificate
You would need to complete your coaching session paperwork, which woul mean running a number of sessions, which would be difficult without some kind of venue or club structure behind you.
The Level 2 course relates to generic cycling techniques and specialist knowledge, such as road racing/time trials, MTB, BMX, track is supplied by additional modules on those subject.
You'll also need to address the questions like:
How likely people are to trust a 19-year old's knowledge?
Where would you coach them?
On the other hand, if you want to earn some beer money, then doing the National Standards Bikeability trainer course is more likely to lead to earning opportunities with local councils, health trusts, etc., teaching (largely) youngsters of 10+ and some adults. There would also be opportunities to teach safe road cycling to adults/families on a private basis, with fees being negotiable.
Suggest you do much more research with coaching providing bodies, talking to existing coaches (list of nearest from BC or ABCC).
If you decide to go ahead, welcome to the club