When do you need a wetsuit?

When do you need to start wearing a wet suit?

This depends on the water temeprature, air temeprature, wind etc... Generally you put on a shorty when the water temperature drops between 72F–77F / 22C-25C and the weather is not that hot.

I suggest that you check out the What wetsuit do I need post. There you will find a full wetsuit temperature guide.