For me, Felix Mendelssohn is the greatest teenage composer ever, and it isn't that close. Mozart is famous as a child prodigy, and wrote a lot of lovely music as a teenager. But it pales in comparison to his mature work and very little of it is performed these days. Schubert invented German Art Song as a teenager, and that is certainly a thing, but in the greater scheme it is not a very big thing. Mendelssohn wrote masterpieces as a teenager: The overture to A Midsummer Night Dream, the Octet, and the A Minor String Quartet, Opus 13. It is (likely) a riff on Beethoven's great, late a minor quartet which was still widely considered the ravings of a crazy person when Mendelssohn was young. And it is as great a work as any romantic string quartet written by anyone.

16/44 FLAC download
Most everything the Talich Quartet touches turns to gold, and it's Mendelssohn Quartets are no exception.