This is simply false. *ALL* registered volunteers have a background check. This is conducted by the local Council, not the unit. The unit simply turns in the signed applicaton form to the Council.
As to the OP's question, I do not know if there is a statute of limitations on certain crimes (i.e. even as a retired cop who spent time in my department's drunk driving enforcement unit, I don't care if a volunteer got arrested for DUI in 1976. If it happened last week, we have a problem...). All crimes involving children will make a volunteer ineligible.