Age 20-40 according to Erikson. There are many variations in defining adulthood, due to differences in psychosocial growth factors. This period is considered to be the healthiest period in your life, ideally in the best shape. Women reach peak fertility during this time period, in late 20's to early 30's. This period of time is crucial for identify formation, determining who you are. Although I am still in this phase, I know I am very independent and motivated for success.