Growth and maturation: why two children of the same age don't perform the same

Two players born in the same year can be years apart in their development. What happens with the growth spurt, which abilities to train at each age, and how not to get it wrong when judging talent.

Linkalde · 2026-10-19

In any youth team there is one player who looks like an under-16 and another who looks like an under-9. Both have the same birth year on the registration form, but not the same biological age. Carlos Borzi puts a number on it in his book on children's football: between the age on the ID card and the biological age, differences of up to 6 years can be found. And that gap explains many of the differences in performance between children of the same age.

For the coach this has two consequences. First, you can't treat everyone the same: the same strength or endurance exercise is gentle for one and too much for another. Second, the one who wins every duel today isn't necessarily the most talented, and the one who loses them today isn't necessarily the least.

The stages of growth

FIFA manuals describe two growth “peaks”: the first in childhood and the second in puberty. Between them lies what they call the golden age of learning, from 9-10 to 13-14 years, the best time for technique, basic tactics and coordination.

Girls usually reach each stage earlier than boys. Borzi places the start of puberty at around 12 years in girls and 14 in boys, and FIFA brings forward the best ages for speed (13-14 years) and strength for girls.

The growth spurt: taller, but clumsier

The second growth peak changes a player in just a few months. According to Borzi, height, leg and arm length and weight increase so much that boys become slower, weaker and clumsier for a while. Technical learning slows down and sometimes stalls. At the same time, strength and endurance rise sharply, and they love that.

• Be patient with technique. The player who used to control the ball beautifully and now can't get anything right hasn't got worse: their body has changed size. Keep working on technique and coordination even if you can't see the progress.
• Coordination and flexibility. FIFA recommends them right in this phase for boys who have grown very fast and have imbalances between muscles and joints.
• Careful with loads. Between 12 and 15 the musculoskeletal system is still fragile. No weights: strengthening is done with body weight, focused on core and back.
• Games before long efforts. At this stage they tend to reject intense tasks they don't enjoy, but they are still hooked on the game.

Which ability to train and when

Each physical ability has its best years for training. FIFA's youth football manual sums them up like this for boys (for girls they come earlier):

A few notes on the chart: flexibility is at its best between 12 and 14 years; speed has a second window from 13 to 15-16 years; coordination is at its best up to 12; bodyweight strength centres on the trunk, and specific strength starts with light loads, between 12 and 20 months after the growth peak.

Two ideas to take to the pitch. First, with the little ones speed and coordination belong in every session, almost always with the ball: FIFA asks for every youth training session to include some element of speed. Second, “pure” physical work comes late: until 15-16 years the physical side is built into the exercises with the ball, and planned fitness training belongs to the 16 to 18 stage.

Endurance in children

Before the age of 10, endurance training increases neither heart size nor oxygen uptake, according to the studies Borzi cites. The child improves because they run better and use oxygen better, not because their engine changes. That is why anaerobic efforts (short, very intense bouts until exhaustion) make no sense in childhood: a child's body isn't ready for them yet.

Don't confuse early maturing with more talent

The early developer wins duels through strength and speed, without needing technique or reading the game. If the coach gives them every minute and sidelines the one who is still small, they can lose both: the first because they never learn to solve things another way, and the second because they get bored and quit before they've grown. FIFA insists on respecting each child's age, growth peaks, learning pace and potential.

1. Look at how they play, not just what they win: orientation of the first touch, decisions, body shape, communication.
2. Share out the minutes. The late developer needs match time so as not to fall behind.
3. Challenge the early developer: fewer touches, playing against older players, positions where size alone isn't enough.
4. Make groups by level when the exercise calls for it, not always by birth year.
5. Talk to the parents: explaining that the growth spurt will come, or that their child is ahead only for now, avoids a lot of frustration.