You can look up the 11 ways we age. They include declining ability to repair DNA, declining ability to make accurate copies for translation into protein, and much more. We have lifestyle diseases that poison us with too much sugar, alcohol and fat. Our bodies were not evolved for such plenty. Evolution cares most about the next generation and older ones just get in the way and hog resources. Sexual reproduction reshuffles the genes to make the new generation best able to cope with the environment as it is and that's the workhorse of evolution. BTW Ben Franklin lived to about 84, I think.