Grip strength and balance can be trained. Each will improve when trained. Improving each metric will help in avoiding death, which leads to longevity.

If you have a better balance, you will fall less. If you have better grip strength, you can catch yourself better if you do lose your balance, which reduces injuries.

Higher grip strength usually correlates to higher strength overall, which leads to fewer injuries.

If you train and eat healthy most of your life, you'll live longer. Balance and grip strength are just two factors in that equation.