Can I volunteer at a hospital if I had a DUI at 19?

In Australia, if you haven't received a conviction you won't have a criminal record. I'm not sure about the States, but I am guessing it's the same in America. If you were done for alcohol or drugs (none of my business) you usually just lose your licence and have to go to court. Unless you are convicted of a felony or misdemeanour you won't have a record. Criminal records are for people who are convicted of offences, not traffic infringements. Make sure, but I think you'll be fine.