To an Older Coworker: “I didn’t know you were so old!”
This comment might come from an initially innocuous and complimentary thought, as in, there’s no way that person is that old — she looks so young! But saying this out loud or expressing shock at an older nurse’s age might turn out to be extremely offensive to them.
Before gasping or widening your eyes, put yourself in your coworker’s shoes and think about the intent of your statement. If you’re just trying to say your older coworker looks good for her age, just say so. “You look great for your age!” will be taken far more graciously than “I didn’t know you were so old!”