This question was asked by a reader in New Zealand. Here is my response:
Most companies these days (TaylorMade, Ping, Callaway, etc.) do not make many “stock” options in steel shafts in a senior flex and never make a stock steel shaft in ladies flex. The reason is that the lightest steel shafts are roughly 75-80 grams in weight (True Temper GS75) and to go any lighter than that in steel is virtually impossible. So most manufacturers will put an 80-85 gram steel shaft in their irons in Regular and Stiff for men and then go to a 65 or 75 gram graphite shaft in senior (usually designated as M or A flex). For ladies there are virtually no stock options in steel. You will see a standard 55 or 65 gram graphite shaft for ladies in irons. Now, when custom building a set, we can pretty much do whatever fits the client, so building a steel 75 or 85 gram iron shaft in a ladies or senior flex for men is fairly straighforward.
As you go down in flex from men’s regular to men’s senior and then to ladies flex, the shaft should feel softer in your hands, you usually will get a higher ball flight as most light steel shafts have soft tips to get the ball airborne. If the shaft is too soft for your swing, your contact will become erratic, shot dispersion will increase (maybe a few more pull shots), and the club may feel too whippy or mushy in your hands.
Not sure if you have some qualified fitters in your area or access to a launch monitor, but that would help quite a bit for me to give you a little more guidance as to what may fit you the best.