a brief history...
My wife and I became vegans when we were in our early 30's after reading "Diet for a new America". Nearly 30 years later we are still vegans. Originally it was (and still is) for ethical reasons, but then we noticed a multitude of health benefits. Joints more flexible, mental alertness, never ever constipated, lost weight, and our blood panels are 100% normal.
Now that were in our late 50's we've noticed everyone else in our age group frankly appears to have burned out. Fat, stiff, blood panel numbers through the roof, on all sorts of medications, etc. Basically they look and feel like crap. We got tired of sharing our diet with people because there's so much defensiveness, and hostility. Really weird. It's always the same. "How can you not eat? I can't imagine not eating meat!", "OMG, not even cheese? I would die without cheese!"
A couple of years ago I had a complete physical and the doctor came back with "well, your numbers look great, but I'm concerned about your diet." I was looking at her (she was my age, 57 and about 80 pounds overweight) while she said this. I was so astounded that I couldn't speak. I was thinking "you are going to sit there, morbidly obese, and tell me that you're concerned about my diet?". Wooah, doctor. Heal thyself!