There are many ways to engineer mammalian metabolism for greater longevity, and more are discovered with each passing year. Any significant upgrade is likely to be a greater challenge to deploy in humans than repairing the metabolism we have, however. Here's a more impressive than average new example of engineered mice; these overexpress PEPCK-C, or Phosphoenolpyruvate carboxykinase. Note that the full PDF-format paper is freely available: "These mice were seven times more active in their cages than controls. On a mouse treadmill, PEPCK-C mice ran up to 6 km at a speed of 20 m/min while controls stopped at 0.2 km. ... The PEPCK-C mice eat 60% more than controls, but had half the body weight and 10% the body fat ... In addition, the number of mitochondria and the content of triglyceride in the skeletal muscle of PEPCK-C mice was greatly increased as compared to controls. PEPCK-C mice had an extended life span relative to control animals; mice up to an age of 2.5 years ran twice as fast as 6-12 month old control animals. We conclude that over-expression of PEPCK-C repatterns energy metabolism and leads to greater longevity."

Link: http://www.jbc.org/cgi/content/abstract/M706127200v1