Yes, you can use 03, 04, etc with a 0 (zero), not the letter O. You will see it like '03, '04 and so on, which makes it more clear that you are referencing a year by adding the apostrophe ('). e.g. I moved to America in '11 = I moved to America in 2011.

Yes. O, is an alternative spelling of "zero". So you can say for example o3(2003), o4(2004), and so on.