I’ve been experimenting with exogenous testosterone for over 15 years.  At almost 73 I have been able to build and keep muscle.  I eat a diet high in protein, lower in carbs and healthy fats.  I take digestive enzymes, and a cupboard full of supplements for anti-aging and to lower inflammation.  I believe we need to challenge our bodies to move and to use resistance training to keep muscle as we add years.  This helps with keeping good bone density and building a healthy vascular system to help sustain new muscle tissue.  The body is an amazing machine if we challenge it to perform and give it the nutrition to support that effort.