I know people who've received cautions and gone on to receive certain higher levels of HMG clearance above that of a CRB. (SC and DV for those that know the system). It hasn't prevented getting jobs even in the most secure of environments. The key thing is not to lie if asked. That would suggest something you're ashamed of and could be blackmailed with. This is the bigger threat rather than the fact you were once young and got a bit carried away with something.