Complex sentence: Musk's first entrepreneurship venture was a residential painting business with College Pro Painters in 1995, when he and his elder brother, Elon started their second company, Zip2.
Split into simpler sentences: Musk's first entrepreneurship venture was a residential painting business with College Pro Painters in 1995. In that year, he and his elder brother, Elon Musk started their second company, Zip2.