、。
At the age of seven, he had already made his own bow and arrow.
Literal
7-years-old [possessive-の] time [locative-(omitted)], already himself [agentive-(omitted)] bow [and-と] arrow [object-を] made.
A biographical sentence, likely about a historical figure. 自ら (みずから) is a formal reflexive meaning 'by oneself, personally, of one's own accord' — more formal than 自分で and typically used in written or elevated speech. The past plain ~た feel of the ending keeps the sentence biographical-narrative rather than conversational.