Final answer:
By age eighteen, a male is typically at Tanner Stage 5, indicating full sexual maturation and the completion of puberty.
Step-by-step explanation:
By age eighteen, a male should be at Tanner Stage 5 of sexual maturation. This stage signifies full sexual maturity, which includes the development of secondary sex characteristics like facial and body hair, as well as the reproductive system reaching its adult form. Tanner Stage 5 represents the adult stage after the completion of puberty, indicating that the male reproductive system has matured and external genital changes have finalized.