The older you get, I reckon the trick is to remember less is more, definitely don't look as though you're trying too hard ( although you are!), keep the look clean, simple fresh and modern. Agree completely re good bra and good haircut. I reckon then you can get away with most things (just not all at the same time!).
Oh and stop believing everybody else is scrutinising every inch of your body. If you've got good legs and 50 year old knees, so what! An above the knee shift dress with tanned legs is a fab look. The rest of the world is getting on with it's own business and definitely not interested in the age of your knees!