Biological age determination is an important activity. Growth and maturation within puberty is a period in which dramatic changes occur in the timing and tempo of a growth spurt for an individual. Calendar age and biological age can thus be very different, and biological age seems more appropriate in assessing development.

Consider, for example, the physical characteristics of two 14-year-old children: a boy with an early onset of puberty and a boy who will reach puberty later with a growth spurt at puberty. The boys will probably have two completely different bodies, although they are training and competing with each other. It is thus possible that in a football team of 14-years-olds, boys compete against each other who clearly do not have the same physical characteristics.

The difference in puberty growth can be increased even further by the so-called ‘birth month effect’, also known as the ‘relative age effect’. Someone who is born on 1st January is almost a year older than someone who was born in the same year but on 31st December. Taken along with differences in puberty growth, the mismatch is increased. You will hear parents who watch a game, saying, ‘This is not fair’: but, irrespective of what a fair game means, this actually is a fair game if you look only at age (i.e. the year of birth).

The children are of the same age after all. However, if you look at them, in physical terms, the parents are right. Physically, it may not be a fair match, and this can misrepresent the outcome of competitive matches. On the other hand, some bigger children may be disrupted in terms of coordination due to their growth, and smaller children may be quick and agile in their movements. In this case, accelerated growth can be seen as a disadvantage rather than an advantage.

source: athleticskillsmodel.com