It may be that because you were a juvenile when you committed the offence that now you are an adult with no further convictions the crb check may not show your juvenile history.
The only true way to find out is to apply yourself and see what comes back.
It only costs �10 and you will see what the employer will get and then be able to explain the circumstances etc.
Employers are increasingly being more tolerant of minor offences especially when they are very old.
Are you applying for a social care/ police/ court worker job?
If you were cautioned and not convicted then you can if asked say no if you are asked if you have any convictions as a caution is not a conviction.
There is no such thing as a spent conviction, I recently had to have a crb check carried out on myself as a requirement for a martial arts instructors certificate and the crb check threw up a conviction from when I was 13yrs old I am now 58, it didn't affect the outcome but it is allways best to be honest when filling out the crb form.