Recognize it as that, and you'll have no problems. But begin fixating on the one failure, and you're on your way to a real problem. Also know that a natural decrease in sexual drive will occur with ages. This, too, is normal. Remember, this decrease in libido is a fact of aging, but it in no way diminishes a man's ability to have an erection.
Older men can have erections at the same frequency and strength as younger men.
So, don't let your decreased sexual drive frighten you into impotence. There's really no correlation. And don't let age frighten you. So often both men and women assume they're losing sexuality because they're aging. And even then, you can have a very fulfilling sex life.