Three years at Nea Salamina: what the birth certificate doesn't tell you

Between September 2023 and September 2026 we assessed 298 children in the Nea Salamina academy — 868 assessments in total, some children thirteen times over. This time the question isn't how fast a child runs. It's how old their body actually is, and whether that number agrees with the one on their birth certificate.

The paperwork decides which question we can answer

Biological age can be estimated in more than one way. For almost every child we can calculate how close they are to their growth spurt, using only age, height and weight (the Moore 2015 method). For a smaller group, whose parents also gave us their own height, we can go one step further and say whether that child is maturing early, on time, or late compared with other children the same age (Khamis-Roche). The second method needs one extra piece of paper. Most parents don't hand it in.

In plain terms: for 86% of the roster we can tell a coach "this child is close to their growth spurt." For the other 14%, because their parents' height is on file, we can also tell the coach "and compared with peers, this child is maturing early." That second sentence is the more useful one for team selection — and it is the one we can say the least often.

Biological age catches up with the birth certificate — then overtakes it

We compared each child's chronological age against their estimated biological age, grouped by year of age. The gap is large in young children, narrows steadily, crosses zero around age thirteen, and then reverses.

We don't trust this number before age nine

78 children are in the window right now

During the growth spurt, bones lengthen faster than muscles and tendons can keep up. Coordination temporarily dips and the risk of overuse injury temporarily rises — not because anything is wrong, but because growth is, for a while, ahead of the body's ability to control it.

Without assessment, these 78 children just look like players who have stopped improving. With assessment, the coach knows who they are and what they need: adjust the load, don't raise the demands.

Early, on time, or late — only for the 39 whose parents gave us the extra number

Among the 39 children where we could classify maturity timing against peers, none came out as a late maturer. This is too small a sample to say anything about the club as a whole — but it's worth naming, because early maturers are exactly the children who look "better" at eleven or twelve without being more skilled, and academies worldwide are known to select for exactly that.

The practical read: a coach looking at two twelve-year-olds, one visibly bigger and stronger than the other, cannot tell from the eye test alone whether that's more talent or more growth. For 39 of these children, we can now say which one it is. For the other 245, we still can't — not because the method doesn't exist, but because the paperwork isn't in.

What one assessment doesn't show

The crossover between chronological and biological age, the 78 children currently in their growth spurt, and the gap in what we can say about timing: none of this shows up in a single assessment. It took three years, 868 assessments, and comparing each child not just against their own history but against a model of what growth is supposed to look like at their age.

Data from the 360 Ergometric Tests database, 13 September 2023 – 8 September 2026, athletes aged 5–17 with an active roster status. Biological age was calculated with the Moore (2015) model from age, height and body mass; where available, Khamis-Roche (predicted adult height from parent heights) was used to additionally classify maturity timing. Only the most recent assessment per athlete is shown. Published with the consent of the Nea Salamina academy. No individual data is disclosed.