Each mountain has different requirements and it changes from year to year. For example, my patrol in the past has trained 6 to 8 patrollers a year in OEC and CPR/AED whith no prior experience other than they must have very good skiing or snowboarding skills. Recently the Patrol Director at the mountain has been receiving a large number of new applications from EMTs and AEMTs that also have good skiing skills. With some on hill OEC training (not the full OEC course), these EMTs and AEMTs can then challenge the OEC test. Therefore their is no need to hold a complete OEC course for beginners. Currently for this patrol you will have to be either an EMT or AEMT(paramedic) to join the patrol. But that was not always the case.
Each patrol is different and holds OEC courses at different times. Some patrols hold OEC courses over the summer and others hold courses during the ski season.
Bottom line is find a few ski ares you want to patrol at. Talk to the Patrol Director at that mountain to determine how you can join the patrol. Some mountains need new patrol candidates more then others.