People don't age at the same speed. The variance for age of (non-violent, natural) death is several decades. And you can notice this difference in the speed of aging at an earlier age, too. Some people appear ancient at sixty, others are virile and look youthful at the same age.
I'm a bit over 50 years old, and yet people who don't know my age regularly guess that I am around 40 years old. The youngest I was thought to be was "in my twenties" when I was 45 years old. I couldn't quite believe that, and after repeated displays of incredulity on my part, the other person corrected themselves to "thirty". Today, my skin is still free of wrinkles, I'm slim and physically fit, and my lifestile is that of a 25 year old.
Face to face, much younger people readily accept me as one of their peers, and young women react very open to my approach. In fact my last two relationships were with women both sixteen years younger, and all my friends are between 25 and 38.
But in online dating, where one has to specify one's age, age is the prime selector after gender. Women that are only a few years younger (and sometimes look older than I), consistently sort me out as too old. The common reply (if I get one) when I write to a fourty year old woman is: "I'm looking for a man my age."
Since I am consistently judged to be about ten years younger than I really am, is it appropriate to specify a younger age in online dating?
As I look like I'm fourty, is it okay for me to pretend to be fourty in online dating?
The purpose of this lie is to enable me to get in contact with those women that would positively react to my approach in a face to face situation, instead of the women my own age who don't regard me as their equal due to my age-inappropriate lifestyle.
The other aspect is that I will probably live longer than those people my age who look their age. My greatparents all lived to around ninety, at a time when the average age of death was seventy. My parents are ninety and of good health. They might live to be a hundred. So in a sense I am not fifty in the same way than some other fifty-year-olds. Giving my "real" age would actually be misleading, if you consider age as indicating the state of one's health and the lifespan one has left.