Qualifications
It really doesn't take much to become an orderly. It's one of those jobs you can apply to right out of high school. So yeah, you'll need to have at least a high school diploma. Other than that, you may need a basic life support certification, otherwise known as a piece of paper that says "I know CPR, I swear!" But even that isn't always necessary. It's pretty much sink or swim during your on-the-job training (source).
If you're a show-off, you can complete a state-approved education program and take a competency exam to become a Certified Nursing Assistant. It's just like being an orderly, but you get to do more things (source).