How often should one buy new irons?

For dedicated golfers and practicers, more than 150 rounds per year and consistent practicers, one should consider replacing their irons every 2-3 years. The wear on the faces and grooves will dictate this.

As for wedges, every season. If staying with the same bounce and loft and brand, keep the old ones to practice with so the grooves on your playing clubs stay fresh.