My child is smaller and slower than their teammates — should I worry?

Usually not. Children of the same age can be up to three years apart in biological maturity, and a big chunk of early advantage is simply earlier growth. The gap typically evens out as later-maturing children finish growing. Protect their enjoyment and keep them playing while their body catches up.

What is biological age, and how is it different from chronological age?

Chronological age is time since birth. Biological age is how far along a child is in their physical maturation — their growth spurt, in particular. Two children the same chronological age can be years apart biologically, which is why training and selection ideally consider maturity, not just the birth year.

Do late developers really catch up?

Often they do more than catch up. As later-maturing children complete growth, the early size advantage fades and skill and work decide more. In ice hockey, around 40% of NHL players are late maturers versus about 19% of under-16 national-team players — the late pathway is a leading route to the top, not a fallback.

Guides · Growth & Development

Is my child behind? Biological age vs the birth certificate

By Marian Pitel, S&C coach·Published 13 June 2026·6 min read

Short answer

Usually your child isn't behind — they just haven't grown yet. Two children of the same birth year can be up to three years apart in biological maturity, and far apart in size. Most of what looks like "talent" at 12 is really earlier maturation. By the late teens the group reshuffles, and late developers often come through strongest.

Two children, same age, three years apart.

The single most useful idea I can give a worried parent is this: chronological age — the birth certificate — is a weak guide to where a child actually is physically. Two children born in the same year can be as much as three years apart in biological maturity. That can mean a difference of up to around 28 cm in height and 8 kg in weight between two "same-age" kids standing next to each other. So when a younger-looking child is getting outrun and out-muscled, you're very often watching a maturity gap, not a talent gap.

Why the early-maturing child looks "talented" at 12.

Selection at younger ages quietly rewards early maturation. The bigger, stronger, faster eleven- or twelve-year-old gets picked, gets more game time, gets better coaching — and looks more talented as a result. But a lot of that early edge is simply a body that arrived sooner. It tells you very little about who'll be best at 18. This is why I'm wary of hard talent calls before a child has finished maturing: at that age you're often measuring the calendar, not the athlete.

The reshuffle — and why "late developer" isn't an insult.

Here's the part that should reassure you. As late-maturing children complete their growth, the group reorders itself. The size advantage evens out; what's left is skill, work, and how the child was treated along the way. In ice hockey, for example, late maturers make up around 40% of NHL players — versus only around 19% of under-16 national-team squads. Read that twice: the late-developer pathway isn't the consolation route, it's a dominant route to the top. "Late developer" is not a slur. It's often a description of the kid who's still standing at the finish.

At twelve you're often measuring the calendar, not the athlete.

What this changes at home.

Two practical shifts. First, swap the question in your head from "is my child behind the others?" to "where is my child in their own maturation?" The conversation-starter I use with parents is simply: "Has your child had their growth spurt yet?" Second, if your child is an early developer, don't bank on the size lasting — push them to build real skill now, while the advantage is masking gaps. And if they're a late developer, protect their enjoyment and keep them in the game; the body catches up, but only if they're still playing when it does.

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This guide explains development in general terms to help decisions at home; it isn't an assessment of an individual child. Any specific concern about growth or health is one for your doctor.