Violist age 15 plays Seitz Concerto in D, first movement
Friedrich Seitz (1848 - 1918) was a German violinist and composer, conductor, concertmaster (first chair in an orchestra), and teacher. He wrote five “Pupil’s Concertos”, as he called them, as a stepping-stone between easier short pieces and the longer, more challenging concertos of Vivaldi, Bach and Mozart. This student is well on the way to completing that transition.
The viola is bigger and lower in pitch than the violin – see also these performances. It loses the highest string (E) on the violin in exchange for a lower one (the C below middle C) at the other end; this, and the greater volume of air inside it, makes for a darker, richer, velvety sound. But the fingering system is exactly the same as on violin, so anything written for violin can be very easily adapted for viola, as has been done here.