It depends on which state the offence was committed, we are talking about indictable offences under the crimes act I presume. In Australia we have a thing called spent convictions, where after 10 years of being a good boy you can apply to the court to have your record spent, which in effect conceals the record. It does not apply to all crimes and not in all states.

"Statute of Limitations" is something quite different. In the US, anyway, It's the time after the commission of a crime after which you can no longer be prosecuted for that crime. Times and crimes vary from State to State, generally, there is no Statute of Limitations on serious offenses like Murder, you could be prosecuted as long as you're still alive.

More to the subject at hand, there is no period of time after whcih convictions drop off your record. Some convictions you may be able to have expunged, the conditions for that vary, but if a conviction hasn't been expunged, it stays for life.

Aviation Security related offences are for the purpose of being issued with an ASIC. I was of the view the posters original question was for the purpose of an employers view of criminal convictions, back in a time when he was young and stupid. The answer to that question depends on the nature of the offence.

420 hours of community service seems light for a serious violent offence. Is there a possibility you are over reacting. Is this a recent thing or distant past.