Original: Crawford, born in the east end of Sunderland, was a keelman until 1786 when, aged 11 or 12, he joined the crew of the Peggy at South Shields as an apprentice.
Simplified: He trained as a keelman until 1786 when he joined the crew of the Peggy at South Shields as an apprentice. He was still only 11 or 12 years old.