329. Covenant construed with reference to original condition of premises.

Every covenant to repair must be construed primarily according to the words used1, but having regard to the age and nature of the premises at the commencement of the lease2. In the case, however, of a covenant by the tenant for general repair (such as a covenant to repair the demised premises and to yield them up in good and substantial repair and condition3, or to keep and leave them in good and tenantable order and repair4, or as often as occasion requires well and substantially to repair, uphold and keep them, and the same so well and substantially