Wolfgang Amadeus Mozart (1756‑1791) is probably the most famous composer of all time. But how much do we really know about him, and how do we separate reality from myth? After all, even the name by which we know him is inauthentic: he was baptised Wolfgangus Theophilus Mozart – Theophilus being the Greek form of Gottlieb, his godfather’s name, meaning “beloved by God”, and although Mozart referred to himself as Wolfgang Amadé throughout his adulthood, he was never known as the Latinised “Amadeus” during his lifetime. We have a partial appreciation of his music, too, as fewer than a quarter of his works are regularly played and a large proportion of those are mostly neglected.

Mozart seems not to be interested in writing tunes but plays with the orchestra as if it were a new toy

At the start of last year I embarked with my company, Classical Opera, on an ambitious 27-year project called Mozart 250. This follows the chronological trajectory of Mozart’s life and works, exploring the music he and his contemporaries wrote exactly 250 years ago, beginning with his childhood visit to London – where he wrote his first symphonies and arias – and ending in 2041, on the anniversary of his death. I am not someone who enjoys knowing exactly what I will be doing in two, five or 10 years’ time, but there is something liberating about the idea that, all being well, we will be performing Idomeneo in 2031, the “Jupiter” Symphony in 2038 and Così Fan Tutte in 2040.

This chronological approach helps us to understand where Mozart’s music came from, and to view his early works in relation to what was being written at the time by other leading composers, rather than making inevitably unfavourable comparisons with the towering masterpieces of his later years. After all, like Shakespeare before him, Mozart was not only a genius but also a child of his time, and not even he could have written Don Giovanni or The Magic Flute in the 1760s, even if he had been born 25 years earlier. The world was not yet ready for them.

Apollo et Hyacinthus KV 38, written by the 11-year-old Mozart

Every year of Mozart 250 begins with a concert that gives a general overview of music composed or premiered 250 years earlier. This month’s retrospective concert of music from 1766 is framed by two symphonies by the 10-year-old Mozart. It also features a dynamic symphony in G minor by Johann Baptist Vanhal and the first movement of a symphony by Franz Ignaz Beck, whose extrovert and unpredictable individuality would later echo Beethoven as much as Mozart. Among the vocal works are a song written for the London Pleasure Gardens by Johann Christian Bach, youngest son of the great Johann Sebastian, and the exquisite “Et incarnatus est” from Haydn’s Missa Cellensis, as well as two charming Mozart concert arias and arias from neglected Italian operas by Pietro Alessandro Guglielmi and Niccolò Jommelli. The Jommelli is especially interesting and beautiful – he was regarded by his contemporaries as one of the greatest opera composers of the day – and in April we will be presenting the UK premiere of the opera in question, Il Vologeso.

Listeners can decide for themselves how Mozart’s early compositions compare with those of his older contemporaries. Certainly they don’t suffer by comparison. What also emerges is a lost musical world of great vibrancy, variety and charm, populated by intriguing but forgotten footnotes of musical history.

Johann Nepomuk della Croce’s painting shows Wolfgang and his sister, Nannerl, with their father, Leopold. Photograph: Corbis

So how did the young Mozart fit into, and ultimately transcend, this world? Over the years, he has been romanticised as the ultimate child prodigy, and stories abound, many of them from reliable sources, about this astonishing boy wonder who could sit at the keyboard – his feet not reaching the floor – and, with phenomenal facility and taste, play blindfolded, or sight-read even the most difficult music, improvising at great length on any given theme.

Were his earliest compositions similarly precocious and ostentatious? What can we learn from them? By way of example let’s consider the beginning of his Symphony No 1, which we performed several times last year. It was written in the then rural calm of Chelsea when the composer was eight, and starts with a short fanfare. This bright, arresting opening immediately commands our attention but could have been written by any number of contemporaneous composers. Within five seconds, though, Mozart diverts us into a hushed series of suspended harmonies, each dissonance resolving to a consonance in a soundscape that, in its own very modest way, is quite different from any symphony that had previously been written. Mozart seems not to be interested in writing tunes, but instead – in keeping with his age – treats the orchestra like a new toy. He plays with it and tests how far he can push the ensemble without breaking either the rules or the piece itself.

There is a range of paradoxes at work here: the music feels derivative, like a faithful and accomplished copy of the work of his peers, yet it already has its own distinct voice and individuality. It is truly remarkable that an eight-year-old could have written such music, yet it is not altogether surprising, given the level of teaching and experience he had already received from his father and from his travels. This is music of its own time, but also music for all time, the burgeoning of a composer who by the end of his short life would have created some of the cornerstones of western civilisation.

Conductor Ian Page. Photograph: Benjamin Ealovega

And then there is Mozart’s Symphony No 3, dating from 1765, a rich, magisterial work that could be called the greatest of all Mozart’s early symphonies. Or so thought the Austrian musicologist Ludwig von Köchel when he came to compile his complete catalogue of Mozart’s compositions in 1862. Actually this work was written by the German composer Carl Friedrich Abel, but the young Mozart was so impressed when he heard it performed in London that he wrote out a fair copy of the score. It was this surviving manuscript that prompted the erroneous attribution – an embarrassment for academics, no doubt, but also a salutary reminder that great artists do not work in a vacuum.

So how much of Mozart’s greatness derived from hard work and an exemplary musical education, and how much from a God-given talent prophetically implied by the name Gottlieb, or Amadeus? The truth is that the two types of greatness are interdependent: he had to nurture his tremendous natural talent by, for example, copying out the work of others.

Mozart himself, though, might have disagreed. There is a story – possibly apocryphal – that towards the end of the composer’s life, a young student asked his advice on how to write a symphony. Mozart said: “It is a difficult and complex form. I would suggest that you first write a few keyboard sonatas, and maybe a string quartet or two, before you start thinking about writing a symphony.”

“But Herr Mozart,” the student insisted, “you were writing symphonies when you were far younger than I am.”

Mozart replied: “I never asked how.”

• Mozart 250: 1766 – a Retrospective is at the Wigmore Hall, London W1, on 19 January.