Final answer:
Adults reach their peak physical performance and development during their 20s, which is deemed early adulthood. This stage is marked by maximum levels of muscle strength, reaction time, and overall health, as well as achieving personal and professional milestones.
Step-by-step explanation:
During their 20s, adults reach their peak in physical performance and development. This period, known as early adulthood, generally spans the ages of 20 through the early 40s. At this stage, individuals often achieve the greatest levels of muscle strength, reaction time, sensory abilities, and cardiac functioning. For many, it's also a time of significant personal growth as they complete their education, establish careers, and form intimate relationships, possibly starting families of their own. Females in their 20s are at their peak fertility, although it starts to decline in the 30s.
Despite the increase in responsibility and complexity in life, health issues tend to be minor for most, and the common causes of death are not due to age-related illness but often external factors like accidents or violence.