Complex sentence: He was known as a child prodigy ("illui") and as a teen-ager attended the Kaminetz Yeshiva headed by his uncle the renowned Rabbi Baruch Ber Lebowitz.
Split into simpler sentences: He was known as a child prodigy ("illui"). As a teenager, he studied at the Kaminetz Yeshiva headed by his uncle, Baruch Ber Lebowitz.