Complex sentence: He made his first stage appearance at the age of eleven as a support act for Swiss singer Helen Vita and was first on television aged 16, alongside the RIAS-Tanzorchester, then under the direction of Horst Jankowski.
Split into simpler sentences: He made his first appearance at the age of eleven as a support act for Swiss singer Helen Vita. He appeared on television for the first time aged 16, alongside the RIAS-Tanzorchester, then under the direction of Horst Jankowski.