Do I need a legal guardian at age 17?

I'm 17 years old, and my only legal guardian just passed away. I live with my grandparents, but my grandmother was my only legal guardian. She recently passed away, but my grandfather says that because I'm 17, it wouldn't do any good for him to become my legal guardian since I'm turning 18 in January. I feel like I need a legal guardian because I'm still a kid, but that's the only reason I can think of...are there more reasons for me to have a legal guardian? Like, medical reasons or something? And it's not like he's kicking me out or anything, he just tried to be put on the guardianship before, but his lawyer totally screwed him over and took his money and didn't do anything. He doesn't want to go through that again, but I can't help feeling that I need a guardian for legal reasons (or something). Do I?