The vast majority of employers have no access to CRB checks. They're only available under specific circumstances, when the provisions of the Rehabilitation of Offenders Act don't apply.
However any CRB check will show any cautions the person might have recorded against their name on the Police National Computer. Up until last year the police used discretionary powers to delete certain minor matters (such as cautions against minors) from the PNC after a certain period of time. However, following a High Court ruling last October, the police now retain all information on the PNC until a person's 100th birthday.
Even if you did apply for employment where a CRB check was required, it's probably unlikely that your caution would be deemed relevant. The only exception might be for getting into the police force. (35% of all UK males acquire a criminal record before the age of 30. There would be a massive gap in the workforce in anyone who'd ever committed a crime couldn't get work!).
Relevant links:
http://www.crb.homeof...els_of_crb_check.aspx
and
http://www.crb.homeof...riminal_convicti.aspx
Chris