I personally do not celebrate them---mine or anyone else's, as a matter of personal faith. My focus is on my eternal life rather than my years on this earth, and I see no reason to celebrate them like it's an accomplishment or a blessing to be a year older. What I consider to be an accomplishment is living my life for the Lord and fulfilling His purpose for me in my years on this earth, however many or few that may be. And I'll celebrate having done this when I get to heaven.
Well, if it walks like a duck, and quacks like a duck, it's a JW.... I mean, a duck...