"There can be little doubt that Gainsborough was born with a precocious intelligence and a God-given ability to paint. Attributing the work he produced in his teenage years has been slow and no doubt unidentified examples will appear in the future and help to clarify his development as an artist. The majority of scholars have accepted this portrait which will be offered at the Cheffins Fine Sale as autograph, perhaps his very earliest extant portrait, and it has been widely exhibited and published.
Dating this portrait has been difficult and it seems most likely that it is one of his earliest attempts at oil painting made soon after he moved from his native Sudbury in Suffolk to London in about 1740. There his apprenticeship was with a silversmith and his skill as a draughtsman was honed by engraving inscriptions and coats-of-arms on the side of silverware. It was not long before his abilities caught the eye of Francis Hayman, the French draughtsman, Hubert Gravelot and the most original artist working at the time, William Hogarth. It must have been these associations that encouraged him to turn to painting.
Gainsborough then moved to Bath in the late 1750s, his style responded to the market around him and it progressed with extraordinary speed. There is every reason to believe that a similar acceleration in the development of his work took place twenty years earlier. In the last ten years a number of canvases have been connected with his name and his earliest years as a painter and they reveal a path towards the well-known portrait of the Revd Hill’s dog, Bumper, dated 1745, now in a private collection in Norfolk. In this small painting the colour sings, the immediacy of the image shows great technical virtuosity but there remain uncertainties of composition and the background has a conspicuous absence of any middle ground.
When considering the painting offered by Cheffins, the delicate and almost emaciated facial features of Gainsborough as seen in his Portrait with wife and child dating from c. 1746 in the National Gallery and the self-portrait drawing from the following decade in the British Museum are close enough to those in the young boy depicted, to confirm the identity and the attribution to the artist. In 2001, specialist Rica Jones made a thorough technical examination of the self-portrait and linked the technique used by the young artist with later uncontested paintings. She discovered that there are two other images painted beneath the present paint surface, the first has been tentatively identified as a landscape, and that the pigments used are consistent with those in the palettes of other artists working in the mid-eighteenth century and they all appear in the artist’s later work. While this is all circumstantial (rather than definitive) evidence, it is substantial, and Jones's work provides the final piece of the jigsaw that enables a full attribution of this small panting to the artist. It is exceptionally rare for an artist to produce a self-portrait in oil at the age of 13. Remarkably few artists have ever attempted it."
https://www.cheffins.co.uk/fine-art/catalogue-view,the-fine-sale_186.htm