There is always a debate as to what is an accurate indicator of both age and health. Some think it's BMI (Body Mass Index), others think it is blood pressure or resting heart rate, and two researchers seem to think it's... your grip strength.
According to several studies your grip strength is an accurate indicator of not only your true age but also is a good indicator of future mortality and susceptibility to disease. Think about it this way - if you have strong hands there is a very good chance that the rest of you is strong inside and out. I have always stressed to my athletes that one of the most important thing they can do to improve their athletic performance is to develop a vice-like grip. It commands respect on the field and it might just save your life while hanging from a window ledge waiting for the fire department to show up.
Check out the whole article on the Washington Post website... and go do some grip work! NOTE: one of the best tools to develop grip strength is the Russian Kettlebell. Every workout will challenge your grip strength and endurace while developing strong forearms and arms as well.
BTW - if grip strength is that important then I know of one very popular president who is doomed; shaking hands with him is like wrestling with a dead fish.