high school
You guys are getting scared for no good reason...
it depends on when you attended high school. What they are talking about is not whether you did ALL the years of high school, but whether you completed the mandatory years or not. E.g when I was in high school, it was only mandatory to complete year 10, Yr11&12 were optional. Then it became Year 11.
So as long as you have the high school certificate, you should be fine.
If you DIDN'T finish, being able to prove 'equivalent study' or applicable experience should also be okay. Lots of people might not do Year 11/12 but then go on to Tafe or another college to do a course which mostly counts when it comes to this kind of thing (depending on what you studied, of course)
Don't stress about it!