DEAR MISS MANNERS: I just turned 43. I’ve worked hard to achieve a level of success I’m comfortable with and have taken pretty good care of myself. In short, I am happy to be exactly where I am in life. When my birthday rolled around, a number of people gave sly winks and said, “Oh, are you 21 now?” or “Turning 30?” At first, I responded truthfully that I wouldn’t go back to 21 or 30, as those years were hard and my 40s have been the best years of my life. But this seemed to offend the people in those age groups. What is an appropriate response to these types of comments? I feel like they impl…