Mary, I ride alone almost every day and I'm a middle aged lady too ! Having said that, if your little voice is saying "no"then there is a reason and you need to listen.! All of the sugestions you have recieved about equipment and precautions are right on, but the most important thing is your partnership with your horse. Work on that with your horse and you will gain the confidence to take on the trails, Study Parelli or whatever natural horseman you admire, the information is out there to help you achieve your goal. May the horse be with you!

I board my horse near a former train track now turned trail and I do trail ride alone.  I am back to riding at age 50+ having bought a very well mannered Tennessee Walker.  I think one key to safety is to have a cell phone - on you not the saddle   Have a reliable horse with whom you have an established trust- you must trust each other!  Let someone know where you are going.  I carry layers for weather changes, water, and a hoof pick for even a short outing.  This is my favorite type of riding and I know my "Angel" is rock solid and does not shy away from vehicles, bicycles nor dogs.  Most others on the trail give right of way to the horse.  If I waited to have a riding buddy I would get few opportunities!  Be safe but don't over  think it- its a beautiful world to see from horseback.