About thirty years old
When he began
Καὶ αὐτὸς ἦν Ἰησοῦς ἀρχόμενος ὡσεὶ ἐτῶν τριάκοντα,
This saying is unique to Luke. He was the only one of the gospel writers who put an age on Jesus. He said that Jesus was about 30 years old when he began his work (Καὶ αὐτὸς ἦν Ἰησοῦς ἀρχόμενος ὡσεὶ ἐτῶν τριάκοντα). Perhaps this is an allusion to King David who was 30 when he became king in 2 Samuel, chapter 5:4. For some the age of 30 was considered mature. Anyway, this concept of Jesus being about 30 with a 3-year public ministry put his death at age 33, a common Christian tradition.