All I can say is ease into it while not letting the thought of if there's any romance there or not consume your mind. Think about it too long and you might miss your chance. Sometimes, it's best to either test the waters or just dive right in. The best that can happen is that there is romance and the worst is...well, there is no worst if you two remain friends at least. Experiment and just go for it. You'll never know unless you try.
I wish you the best of luck.
P.S.
You said that you've known her for over 16 years now, right? If you tried something then but it never took off, then maybe you two weren't meant to hook up at that time, with life wanting you two to mature a bit more in real life experiences before trying again and possibly creating a romantic connection.