The problem, simply put, is that you are old. Employers will believe that you have outlived your use and that you don't have the energy of the younger salespeople. What you need to do is convince your potential employer that even though you're showing signs of gray hair, you still have what it takes to hold your own on the sales floor.
First of all, you need to put the concept of being old behind you. Yes, you are old, no, you can't hide it effectively, but if you want to find your place in sales jobs you need to have confidence. That is to say confidence that you will be able to do your job. If an employer sees that you are confident in yourself, then there is a greater chance they will have confidence in you.
Remember though, that confidence does not mean looking down on the younger generation. Chances are you are going to be stuck with a manager that is twenty years younger than you, and you need to make sure that you are willing to work with them, rather than trying to lead them. Jobs in sales required that you play as a team. Rather than having the opinion that you know everything, show that you are willing to learn. One of the biggest problems for older individuals in the workplace is that they appear to be for the most part completely untrainable.
Now you need to make your age seem like more of a positive than a negative. How do you do this? Well if you think about it, jobs in sales and sales careers require some measure of experience. As someone who has spent an enormous amount of time in the workforce, you definitely have the experience. You can assure them that you have the skills and the willingness to work with people of all ages and that you have a good work ethic. Of course, you have a good work ethic. You wouldn't have made it this far without one, would you?
When trying to get into sales jobs, make sure that you don't focus on career accomplishment that are more than ten years old. The reason is that times have changed, and the achievements you made back then might not really have any relevance in today's world. Rather you should focus on the achievements you have made today. Make it sound as if you are familiar with the way things work today, which is extremely important in sales careers.
These are things that you should have on your resume as well. Make sure that you detail everything that you have done within the last ten years, and also put down that you would like to work in a fast paced environment. As you know, today is nothing BUT a fast paced environment. Work hard, and make sure that your resume catches the employer's attention from the start. At this point, your word, your resume, and your experience are all you have. Make them good!