It?s generally recommend that males wait until they are 25 years old to us AAS. Prior to this age, your average male's HPTA and endocrine system are still developing. Using AAS prior to age 25 can be very harmful to these systems and result in permanent damage. Studies have shown that there are permanent reductions in Total Testosterone levels as a result. ED and fertility can be affected. Some guys never recover properly and have to go on TRT for the remainder of their lives. And running AAS prior to age 20 will likely result in fusing of the growth plates.