For me, 40 was the hardest. I can't get away from feeling that the 40 years are that horrid moment when you are no longer young but not ready to be middle aged. Yet anyone under 25 looks upon you with horror and are in no doubt that you are, in fact, middle aged.
By 50, you have turned a corner. No one is in any doubt that at 50, you are middle aged, and somehow it is easier to embrace. Maybe it is because you are suddenly free of encumbrances. I went through the menopause at 50. It is fantastic not bleeding every month, I am glad that the perimenopause (which for me, was long and trying) is over. I still have one child at home, but he is nearly 16 and no longer tied to my apron strings. Maybe, there might be more money to do things, there is certainly more freedom to do them.
I did a few special things in the year I turned 50, planned treats for me, and really enjoyed doing them. I have met a few retired people and seen how much enjoyment they are getting from life. My own peers are beginning to talk about what they will do in retirement, fantasizing that they might start retirement a few years early (I doubt they will, but it is fun thinking about it). There is a growing sense that if we don't get on enjoying life, time will run out for us. That is a positive, when you think about it.