Question Author
You bet.....learning anything at any age is beneficial, but I make the plea for language acquisition while the L.A.D. is operating, from birth (literally) to age 11 years. There is a bonus - seemingly the L.A.D. has no limits. Children reared in polyglot societies acquire all the languages to which they have been exposed, and speak them fluently.
In Israeli kibbutz, kids reared by a multiplicity of surrogate mothers, of many nationalities, were found to be fluent in 7+
languages.
In bilingual households, Welsh / English perhaps, the children simply absorb both with no effort. Lucky, lucky children ; they can think in ways denied to others, since as Wittgenstein said : 'My language defines my world '