I just checked my flight history, and noticed I flew OZ on my last birthday. I was in C and they didn't give me any cake and didn't even recognize that it was my birthday. Not that I care personally, as I'd likely feel someone awkward if they came out with a piece of birthday cake for me on the plane.

I didn't mention to the FAs that it was my birthday, so maybe if you want some cake or other special treatment you could mention it to them and see if they give you anything special.