...and it may not be what some others have posted, but here goes.
I say GO FOR IT!!!
My reason for it is simple....I dont know if your lucky enough to make a yearly trip, but for our family, going to WDW is about as special as it gets...we have been lucky enough to go once every few years, so, when we get down there this year, each of the kids will have a day designated as their "UN-birthday".
What I plan on doing, is go from most recent to furthest away.
Is this ok...of course it is.
I could understand an adult feeling funny about it(mind you, neither my wife nor I will have this marked, but.........
I do plan on getting in an anniversary day for my wife....I dont think she'll mind a little extra magic given her for our day, which is in April(we are going in MAY)
With that said, I dont think that the Disney folks are going to mind anyone celebrating their birthday(or any other special occasion) a week, month, or shoot, 364 days early....its not as if your celebration for your own child is going to put anyone out.
One thing that I MUST add, is please dont expect that anything"extra" WILL happen...its all the call of the CM's...in other words, if you get front of the line, AWESOME..if they(CM's) come out with a few balloons, EXCELLENT..Ive even heard tales of folks almost getting red carpet treatment all day...this would be welcome, but if you get hopes up too high there will be some disappointment.
If getting the pin(which is cool to have)will make your kids day,or visit extra special, then that is on the list.
If you know your kid will be in the "whatever" state of mind, then it may not be as special.
I know my kids will enjoy the little bit of attention they get...and honestly, when you really think about it, I think that all kids deserve to have all the magic they can...they are kids for only so long.
Get the pin, and tell your boy happy birthday from us!!!!!!!