The brain is the last to develop fully, which is around 24 in males.
The metabolic rate does change with the development of an animal from a zygote to adult because of the development of the organs. As growth occurs the organs fully develop.
The lungs are the last organs to develop in utero. They are generally developed enough to be able to perform breathing at about 32 weeks, or 7 1/2 months.
Once a foetus is fully developed it has exactly the same organs as a fully grown human.
About 17 days after fertilization.
In the first three weeks, the embryo has formed the forebrain, the midbrain and the hindbrain. In your second trimester, the major structures of the brain are in place and functioning. From this point the brain and organs continue to develop.
Research has recently discovered that the brain does not fully develop until the age of 25. It is the cortex of the brain that fully develops at this time.
Definately if it is not fully removed from connecting organs