Most girls are physically fully developed by the age of eighteen. Girls have reached adulthood at the age of eighteen, and most women at this stage are fully developed, including height development, physical development, and the development of female secondary sexual characteristics. At this time, women’s physical characteristics are more obvious, and the development of sexual organs is mature. However, there are individual differences, and there are also a few women who may not have fully developed their bodies at the age of eighteen due to acquired nutritional reasons, such as acquired nutritional deficiencies. If a girl’s body develops abnormally at the age of eighteen, for example, the secondary sexual characteristics are not mature, she should consult a doctor in time to exclude pathological factors. Diet must pay attention to increase nutrition, eat more food rich in high quality protein and vitamins.