How often a fountain pen was written with is largely irrelevant for the condition of the nib: gold nibs have an iridium tipping at the tip that survives many generations of intensive use without measurable change. Statements like "only written in" or "broken in" are from a collector's view rather marketing formulas. The exact age too is mostly not unambiguously ascertainable, since writing instruments are partly stored in trade for years. With B nibs, which are more frequently offered than F or EF, it is worthwhile comparing several offers and not rushing the purchase.