The appropriate shaft flex for a golfer depends on their swing speed. Here are some general guidelines based on the search results:

• Under 75 mph: Ladies flex or Senior flex
• 75 to 95 mph: Regular flex
• 95 to 110 mph: Stiff flex
• 110 mph and up: Stiff or Extra Stiff

For irons specifically, a swing speed of about 95 to 110 mph is eligible for a Stiff shaft. However, its important to note that these are just general guidelines and getting fitted by a professional clubfitter is recommended to determine the best shaft flex for an individuals swing.