Total testosterone declines about 1% per year after 30, but the more consequential changes are vascular: stiffer arteries, reduced nitric oxide and slower recovery. Mitochondrial density in muscle also falls, which is why stamina drops before strength does.
Slightly lower libido, longer recovery, less morning energy. These are age-appropriate and respond to lifestyle.
Sudden loss of libido, persistent erectile difficulty, depression, unexplained fatigue. These warrant blood work — they can signal diabetes, thyroid disease or cardiovascular problems.
Nutritional support for circulation and energy, alongside exercise and sleep. Not a replacement for either.