I retired last year and also thought I would do the personal training thing. I even spent $400 to buy the study materials for the exam. However, as I started studying, I realized that I really didn't want to work in a health club; although there are plenty of trainers my age at my club, generally you don't get treated that well when you work in a gym. This is based on my ten years experience as a group exercise instructor. I thought really hard about what I wanted to do and decided to go back to school to become a clinical mental health counselor. I want to work with people dealing with eating, weight, health issues. Although it is going to take me 3 years to get the degree and another 2 years of working full time to be able to call myself "licensed," I feel much more comfortable in this role.
I am the same age as you and I say do what you want!