を問わず means 'regardless of' or 'irrespective of'. It is used to state that a condition, rule, or action applies to all cases within a category, not limited by the named factor. For example, saying '年齢を問わず' means 'regardless of age', so participants of any age are included. The noun can denote a broad category (like 'age', 'gender', 'nationality') or a pair of opposites (like 'day or night', 'success or failure'). It is a somewhat formal expression, often used in written announcements, rules, or official statements, but it can appear in spoken Japanese when making a general statement. It is not used for personal preferences or subjective feelings, but for objective boundaries or criteria.