If you're going to make it, it's important to learn to tune out the negative, just like everything else. Know why you're doing this. Make sure you focus on your reasons for wanting to transition to grey hair and stay focused. If you really know why you are letting your hair go grey, ignoring the naysayers becomes a bit easier.
So, how do you find your passion after 50 when you've spent your life not really knowing? The easiest thing is to pay attention to that little voice in your head, or your heart. This is the voice that says, "Yes!", when you come across certain things. Focus on that thing that gets you excited, or that thing that you automatically are attracted to whenever you encounter it. It's about the feeling you get whenever someone mentions it, or you see a video about it, or an article. What gets you excited?