Disney doesn't care when or what you celebrate! We celebrated MY birthday in December the whole week, not just the day of the brithday. But in April, we celebrated DD birthday, and it was almost a month away. The pin they give you doesn't say "It's my birthday" it says "Celebrating ____'s Brithday" same thing anniversary. You and DH want to go out to dinner the two of you, tell them your celebrating your anniversary. If it's not, so what, celebrate it anyways.
So, you want a cake, get a cake. Say your celebrating your birthday, your sons birthday, you parents anniversary...whatever you want. Disney doesn't care, they just want to money for the cake!
Link to my birthday cake