Complex sentence: It quickly became apparent that he was a child prodigy, and by the age of seven Fryderyk had begun giving public concerts, and in 1817 he composed two polonaises, in G minor and B-flat major.
Split into simpler sentences: It quickly became apparent that he was a child prodigy. By the age of seven Fryderyk had begun giving public concerts, and in 1817 he composed two polonaises, in G minor and B-flat major.