T drops as men age, metabolism becomes more inefficient each year (My understanding is 1% decline per year) Both mean more fat retention, which promotes estrogen, which promotes further fat retention. Cellular conversion of nutrients into engery declines resulting in compounding cellular damage (currently no way to stop this but a biotech company has claimed to reverse aging in mice with suppliments to energy convserion so there is always hope!). Injuries that would require rest for healing take longer, providing the body more time to decompensate. Unless one is subtly increasing activity and improving diet and somehow boosting testosterone at sufficient levels (not sure that can even be done without steroids/hormone replacement), you are just not going to sustain your age 24 body into your 50's. A few exceptions of remarkable men, but my guess their entire day is filled with activity and they have religious discipline on their diet.