Testosterone levels in men peak in their late teens to early twenties.
This is typically around the age of 18-20 years old.
After this peak, testosterone levels gradually decline with age.
This decline is typically about 1% per year after the age of 30.
However, the rate of decline can vary depending on individual factors such as genetics, lifestyle, and overall health.
It's important to note that testosterone levels can also be affected by other factors, such as medical conditions, medications, and stress.