Does having lumps in the breasts mean they have developed?

Generally speaking, the presence of breast buds does not necessarily mean that breast development is complete. The detailed explanation is as follows:

Breast buds are a type of tissue structure in the female breast, composed of glandular and fatty tissues. Breast development gradually occurs during female puberty. In early puberty, the ovaries begin to secrete estrogen, which stimulates breast proliferation and initiates breast development, leading to the formation of structures such as the nipples, areolae, and mammary glands. The size, shape, and texture of the breasts continue to change throughout this process. The presence of breast buds does not indicate that breast development has finished. During breast development, breast buds are an important component resulting from mammary gland proliferation and consist of glandular and fatty tissues. The appearance of breast buds is one sign of normal breast development, but it does not signify completion of development. Breast development typically completes around age 18, although the size, shape, and texture vary among individuals, and in some women, breast development may continue until around age 20. If signs of breast development persist beyond this age, medical evaluation may be necessary to determine whether there is an underlying pathological cause, such as endocrine disorders.

In addition, breast development is a complex process influenced by multiple factors, including genetics and endocrine function. If signs of breast development are still present around age 18, a medical examination can help determine whether any pathological conditions exist.