Forget about these ridiculous “temperature rules”; 100°,120°, etc. Once you are in the water the air temperature is irrelevant. Although long discredited these rules were proposed by ACA and unfortunately copied by the USCG and many other organizations. Once in print, people are resistant to change. You would think that the ACA would know better being located if Fredericksburg, VA, not far from the Chesapeake Bay. The Chesapeake Bay, with its large surface area and relative average depth warms and cools very rapidly. In the Spring especially, water temperatures still in the 40s and air temperatures in the 80s are not uncommon. Multiple deaths occur every year in the shoulder seasons due to cold water immersion often combined with not wearing a PFD.
Our Club requires cold water gear starting at 60°F in protected waters and higher water temperatures depending on conditions.
How a person reacts to cold water can vary considerably. Temperatures are deceiving. Air at 60° is reasonably comfortable. Water at 60° feels pretty cold to me and tolerable for a fairly short time.
I used to wear a wetsuit down to about 50°, but since I bought a drysuit I don’t wear a wet suit anymore. I find a drysuit more comfortable and versatile. It’s very expensive, but considering many of the top brands have a lifetime warranty, the financial pain fades over time
A wetsuit is more affordable in the shoulder seasons, but bear in mind that a wetsuit by itself is really designed to be comfortable when one is in the water. Out of the water they can be very hot when exercising and not very warm when in the wind on a cool breezy day. You will want some wind and thermal protection when out of the water that you can put on and take off.