It can't be testosterone alone. I've got the levels of a 25 year old according to my urologist (and yes, he sent me to be checked for anomalies) and I've notice

It can't be testosterone alone. I've got the levels of a 25 year old according to my urologist (and yes, he sent me to be checked for anomalies) and I've noticed a significant decline in metabolism after the age of 40, despite exercising and not gaining weight and sleeping more than before. My (unscientific) hypothesis is that it's mostly a mental thing due to work/life being less demanding at this point.