Complex sentence: The parents or guardians of a minor would agree with a Guild's Master craftsman the conditions for an apprenticeship which would bind the minor for 5--9 years (e.g., from age 14 to 21).
Split into simpler sentences: The parents or guardians of a minor would agree with a master craftsman or tradesman the conditions for an apprenticeship. This contract would then bind the youth for 5--9 years (e.g., from age 14 to 21).