What is the best age to start a second language?

"Is it too late?" is probably the most common worry parents have about languages, and adults and teenagers ask it about themselves too. The honest answer from research is more nuanced than either "start at birth" or "age does not matter".

What does the research actually say?

The study most often cited in recent years is a Cognition paper by Joshua Hartshorne, Joshua Tenenbaum and Steven Pinker (Cognition, 2018). It analysed an online grammar quiz taken by about 670,000 native and non-native English speakers. The researchers used a computational model to separate three things that normally get tangled together: how old a person is now, how old they were when they first met the language, and how many years they have used it.

Their main findings, in plain terms:

• Grammar-learning ability stays roughly steady through childhood, then declines steadily from the late teens. Their best estimate for the start of the decline was about 17.
• People who began learning English by about 10 to 12 years old ended up, on average, at levels similar to native bilinguals. People who began later reached progressively lower levels on average.
• The authors conclude that the results support a "sharply-defined critical period", but one that ends much later than earlier accounts had speculated.

You can read the open author manuscript on PubMed Central.

What can't this study tell us?

Quite a lot, and the authors say so themselves. In their own discussion they note that:

• The quiz was written and tested understanding of grammar, not speech, so it may not capture all aspects of language ability.
• People chose to take a viral online quiz and reported their own details, so the sample is not representative of everyone.
• Monolingual speakers scored near the top, which limits precision at the high end.
• The age-17 figure depends on the assumptions of their model.
• Other parts of language, such as sounds and vocabulary, might follow different timelines.

They also raise a point that matters for families. The decline might not be only about the brain. They suggest culture could play a part, because the age where ability starts to fall coincides with big life changes such as starting work or further study, which may cut both the opportunities and the motivation to learn. They say other explanations remain possible and speculative.

The authors themselves list other possible explanations and call several of them speculative. The science here is not settled, so treat any single age as a rough guide.

Does "ability declines at 17" mean learning stops at 17?

No, and the authors take care to separate two ideas. One is the age at which the ability to learn starts to fall. The other is the age at which a person reaches their final level. The paper notes that even native speakers take until around 30 to reach full proficiency in grammar, so the two timelines are not the same thing. In the authors' model the decline is steady rather than abrupt, and a person who keeps practising keeps improving long after the slope begins. That is also why the study's authors point to opportunity and motivation as live possibilities.

So what is the best age to start?

Taken together, a careful reading is:

1. Starting young gives you more time. More years of exposure matters, and children usually have more hours in a day and more years ahead.
2. Starting later is still worthwhile. The study describes an average decline across big groups of people. It does not say a 30-year-old cannot reach a good level. Real people vary a lot.
3. How you learn probably matters as much as when. Hours of exposure, chances to speak and regular review all matter, and the research on those is not about age at all.

A parent-facing review of early bilingualism by two researchers lands in the same place in practice: an early start is a plus, yet the door never closes, and a parent's own limited fluency is no reason to wait (Byers-Heinlein and Lew-Williams).

What about children who start at school?

In NSW, languages are optional in primary school, and students take one language across a single unbroken year somewhere between Years 7 and 10, preferably early (NSW Department of Education). That is when many children first meet a second language in a classroom. If a family wants more exposure than that, home practice can fill gaps. Our plan for learning at home sets out a simple weekly pattern, and our piece on what NSW offers explains the school pathway.

What should an adult or teenager take from this?

Do not let a headline about "a critical period" talk you out of starting. Reasonable steps:

• Pick a language you actually care about; motivation is probably doing real work.
• Aim for regular short sessions rather than occasional long ones.
• Find a way to speak with real people, even occasionally.
• Expect slow, uneven progress, and measure it in small things you can now do.

Looking ahead

XLingo is a languages course for families and adult learners, with eleven languages and six levels each. A teen or adult at your place who wants a calm, step-by-step way in can start with a 7-day free trial; one family subscription covers everyone.