How to tell my wife I don't want to celebrate my birthday

I was born the day after Christmas and my wife lives to throw huge parties. It's her things. She usually makes my party Christmas themed and we celebrate both but this year I just want to forget my birthday. I turn 30 this year and while I'll never admit it to anyone in my personal life I recently started having some depression. I'm married and have 3 kids and just had a vasectomy two weeks ago. The vasectomy was hard in a different way. Not physically, just a little hard mentally. And now that I'm turning 30 I realize I've basically peaked. My best years are behind me. I'm a father of 3 and married. There's really nothing left for me. The rest of my life is really nothing more than waiting around to die. My kids will grow up and leave home. It will be me and my wife and then we die. I rather not be reminded that I'm hitting my peak and my depression has gotten worse knowing I'm getting closer to 30. My wife is awesome and I know she loves birthdays and wants to do this for me but honestly I'm fine with just not having a party and forgetting about it.