Age is a state of mind or just a number?

Yes I know - I am in an enormously immense huge midlife crisis. Three months away from 50 and I look in the mirror and don't see it. I see maybe 40, but not 50, this isn't what 50 is supposed to look like. Why can't I choose my number for the day depending on how I feel and look? Why am I boxed in by chronological age - a number - what does it mean?

That I am supposed to act, or dress, or look a certain way, by whose set of standards and expectations?

Isn't 50 supposed to be all about grey hair and feeling old, or at least that is what it was when I was a child, or even when I was 25. But now, who is 50 - Madonna? She is weird with her diet and whose knows how much plastic surgery, but look at her. Dara Torres, the Olympic swimmer at 42 - her body is amazing. So what is 50, not how I feel or look. Definitely not my state of mind. But certainly wondering and searching for the real meaning of my life, why am I here? What am I supposed to accomplish with my time here because my time is running out, and where is it all headed?

Yes, a real mid-life crisis, and I loudly proclaim that I reject the number 50.