Complex sentence: Thomas was classically trained on the violin and piano as a child and he began playing bass in London pop bands, turning down at one point the opportunity to play with Jimi Hendrix and Mitch Mitchell before Hendrix had struck fame.
Split into simpler sentences: Thomas was classically trained on the violin and piano as a child. He began playing bass in London pop bands, turning down at one point the opportunity to play with Jimi Hendrix and Mitch Mitchell before Hendrix had struck fame.