obesity: Body Mass Index for adultsEncyclopÃ¦dia Britannica, Inc.Obesity was traditionally defined as an increase in body weight that was greater than 20 percent of an individualâs ideal body weightâthe weight associated with the lowest risk of death, as determined by certain factors, such as age, height, and gender.
Define infancy: early childhood; a beginning or early period of existence; the legal status of an infant â infancy in a sentence early childhood; a beginning or early period of existence; the legal status of an infantâ¦ See the full definition
Merriam-Webster dictionary simply says a newborn is a baby who is recently born and does not put an upper limit to the term. The dictionary also defines an infant as a child in the first stage of life but doesn't give any age specifics.