The thing I think everyone should have regardless of age however is a durable power of attorney for medical decisions. This would give someone you trust the ability to "pull the plug" and let you end your suffering if something awful should happen such as a car crash. Without one of these there can be family squabbles with one person saying it's time to let her go and another saying no, and, if that kind of thing is going on, the hospital is legally obligated to keep you alive even if it means shoving a feeding tube down your nose (ick!).
I know, it's not fun to think about. I kind of had to face these realities sooner than most people when I had cancer.
Oh, and about writing a will. You don't need a lawyer at all. Just write it up on your computer, print it out, and take it to a notary public and get your signature notarized and it is a legal document.