Hi there.
There's really no answer to your question, because sexual desire is dependent on many factors, including mood, emotional stability, attitude, general physical health, etc.
It sounds as though you're enjoying sex, and it's a positive part of your life. Good for you! There's really no reason for our sexual desires to diminish with age unless we don't take good care of ourselves. Do that, and you'll probably end up being the sexiest 90-year-old on the planet. Dr. J