Tomorrow Brings 40

Tomorrow brings 40 years. WHAT? I'm 40 years old? It simply can't be . . . I don't think I really look that old. I certainly don't FEEL 40 or ACT 40. What constitutes being 40 that didn't constitute me being 25, 30, 35, 38, 39? I'm a home owner, I have a job, a car, kids, financial stability. I don't feel very good today . . . maybe I'll call in sick tomorrow?