Both Michael and Joanne are spot on if you ask me. The best athletes, no matter how hard they’ve trained over the years, generally owe a huge thank you to their parents for gifting them with such marvelous genes.
Do you incorporate some form of periodization into your training programs? It can be extremely useful for anyone looking to seriously increase their level of fitness (speed included) over time.
I’d recommend checking out the following link for some great HIIT workouts that (when used appropriately over time) will positively effect one’s speed: http://www.12minuteathlete.com/
Hope these help make you faster!