Wetsuit question

No, I am not a wimp-but temperatures below a certain point necessitate additional insulation for me. Having said that, my question is how often do they need to be replaced (even when in seemingly good condition). I have 3 suits of various sizes, paralleling my various sizes over the years, ranging in age from 9-18 years old. Does the material get stiff? My current suit is getting impossible to put on. I have gained some weight, but according to the company's size chart, I am well within it. I could try my old fat suit, but I am wondering if the material is just too old and stiff (like me). There may be some in local stores I could try just to see if they feel stretchier. I wish I didn't need one at all. Very frusterating!...