Wetsuits stretch! wetsuit is made out of neoprene that is a very flexible and stretchy material. So the natural flexibility of wetsuits is quite big. Then there is stretching when the neoprene gets wet - a dry wetsuit is tighter than a wet wetsuit. And finally, I gues this is what you wanted to know - will wetsuit stretch over time? Like any elastic material the neoprene will loose its flexibility in time. If you take good care of your wetsuit this will take a year or a few years (depends on how much do you use your wetsuit). If you don't take good care of it, if you leave it in the sun a lot, it will happen faster.

Neoprene will lose the flexibility and its ability to return to the original state after it was stretched. So your wetsuit will become looser and bigger. This change is not that huge that you should worry about it - like that your wetsuit will not fit you anymore.

If your wetsuit is to small and you are wondering if it will stretch. Huh, it will. If you are to big for a wetsuit you will stretch it. It is hard to tell how much. But this is not the best thing for the wetsuit because it will speed up the before mentioned process - your wetsuit becoming less flexible.