Welcome, Susan!
Oh, my goodness, you are not too old!
I've been on a low fat diet in the past, and had good success.
I've never been big on fruits and veggies, and doing the low fat thing forced me to eat more as alternatives to... well, you know the high fat foods.
Yes, keep walking! A few years ago I was at an all-time high, and found walking any distance difficult. Painful, actually. Don't stop... it gets better, and you'll be striding along in no time.
Beth, my mom is 82, and goes to the gym three times a week. She would say, "78 is NOT old!"