I am 47 and my hair is doing this too. It is pretty long now and the length is pulling it straighter so I am just blow-drying it straight and going for the long,straight-haired look. I think it looks OK. My hair is pretty thick, and I cover the grey (I only have a small amount of grey), so this still works for me. If my hair starts to thin or the grey starts to be too much to keep up with, I'll keep it shorter.
There is nothing wrong with curly,wavy or straight hair.
Be happy with yourself the way you are and work with it. It's pointless and self-destructive to worry that you don't look the way you used to. (Unless it is related to a health problem.)