Those "symptoms" of old age are not a given. I am not 50 yet but I do get a lot of people thinking I am 10 years younger than my age. You do not have to settle for loss of memory and sleepless nights once you hit 50. If you are experiencing these things then I would suggest finding some sort of holistic regimen that will help allay those issues. Yoga would be the first thing I would recommend. You might also want to look into your diet to eat more foods that will enhance the memory. There is no reason why anyone needs to lose their faculties at 50, and if you are I suggest something else is going on than just age. My grandfather lived until 96 and he was sharp as a tack his entire senior life and was still gardening and moving large logs well into his 90s.

Stephanie makes some great points.  I am 51 and last year my wife and I had our entire metabolism checked and re-tuned.  Our energy, mental alertness increased dramatically.  We both lost 30 pounds in the process.  But I would also consider learning some lessons from our oldest adults who are living quality lives into a very old age.  In my keynote The Meaning of Life, I talk about eight things I have encountered in my work with older folks.

Have purpose, stay active, embrace humor, increase your social network, have a great attitude, be grateful, be loving, embrace lifelong learning.