Is it normal to have purple-bluish skin on your feet at 55?

It depends. It is generally not normal but maybe not dangerous. If you have purple-blue feet that are cold and painful when your feet are up and better when your feet are down, see a doctor immediately. The arterial supply in your legs may be dangerously compromised. If you have painful purple-blue feet when your legs are down and the color improves when they are up, it's likely related to varicose veins.