Testosterone production peaks in your 30s and steadily declines thereafter. Since testosterone is the most important hormone for muscle growth, you will need to put more effort into your workout to see the same gains. I have not heard anything about the actual muscle tissue fundamentally change as you age.
Your digestion efficiency also declines as you age. You will be absorbing less nutrients per gram of food as you age. You will need to eat slightly more carbs and protein than a younger person to fuel your muscles.
Hydrochloric acid deficiency is common
in older people and prevents the
proper breakdown and digestion of
proteins, which are critical to
health. Your production of digestive
enzymes also declines with age
affective digestion of all three macro
nutrients (proteins, fats, and