This, my seventh puzzle, is also my first symmetric barred grid. The secret message—instructions on how to fill parts of this grid, and what I'm "celebrating"—can be found at 1A/35A. Many thanks to my test solvers, skaldskaparmal, GandaPestile, and n0hk; any remaining issues with the clues rest entirely on my shoulders.
Happy Birthday and enjoy your forties. Decades get weird when you have kids...