What is the source for the custom of reading the verses beginning “Abraham was old” for a groom in the synagogue?

This Torah study examines the question: What is the source for the custom of reading the verses beginning “Abraham was old” for a groom in the synagogue? The canonical Hebrew discussion develops the issue through the weekly Torah portion and the sources cited there, preserving the distinctions, tensions and practical implications that belong to the source itself. This localized layer is designed for study and discovery; it does not add a new halakhic, medical, legal, historical or empirical ruling beyond the canonical Hebrew source.