Is music your first or second language?

As adults, we cannot understand why are kids starting piano lessons at pre-school ages, even before they talk or read properly!  Is it sensible to take up lessons before their cognitive abilities kick in? 

I have taught kids as young as 2 years old ( not prodigies, just regular 2 yr olds that are crying and wants sweets) , teenagers ( just normal ones that are stressed out by school and relationships) , young adults and middle age adults beginner piano courses.  Generally, intrinsic motivation is higher in grown ups and they pick up the basics extremely quickly.  But, after a period of time, the difficult 2 yrs olds will ease into expressing themselves through musical idioms.  The older students may or may not ever achieve the ability to play in "musical idioms" and musical sentences.

This is related to Critical Period Hypothesis of language learning. The reason why kids that could barely speak will be more fluent in their playing later on is because, music had a chance to become their "first language". Older beginners, ( outside of the critical period from age 5 to puberty) respond to music as a "second language".  They pick it up faster, because of the cognitive and analytical powers of the mind, but may be less natural and fluent.  You can read more on Critical Period Hypothesis below.

Taken from Wikepedia:

The Critical Period Hypothesis states that the first few years of life constitute the time during which language develops readily and after which (sometime between age 5 and puberty) language acquisition is much more difficult and ultimately less successful^[1]. The critical period hypothesis was proposed by linguist Eric Lenneberg in 1967.

The theory has often been extended to a critical period for second language acquisition, although this is much less widely accepted. Certainly, older learners of a second language rarely achieve the native-like fluency that younger learners display, despite often progressing faster than children in the initial stages. David Singleton (1995) states that in learning a second language, "younger = better in the long run," but points out that there are many exceptions, noting that five percent of adult bilinguals master a second language even though they begin learning it when they are well into adulthood — long after any critical period has presumably come to a close. Evidence is controversial the Second Language Acquisition involves a critical period, nevertheless, it is generally agreed that younger people learning a second language typically achieve fluency more often than older learners. Older learners may be able to speak the language but will lack the native fluidity of younger learners. The Second Language Acquisition Critical Period coincides approximately with the Formal Operational Stage of Jean Piaget's theory of cognitive Development (Age 11+).