There are many indicators; some genetic, some environmental, and some mental. Are you generally lean? Were you a good runner when you were a kid? Were you fast for short distances, or did you have long distance endurance? Are you competitive in things you do, or are you lazy and passive? Very simply, do you like participating in active sports?
Unless you're hopelessly sedentary and obese, try riding and getting into reasonable shape. Find a group to ride with. It'll take a few years to get good, and then four or five years of racing to reach your potential. I've seen racers with average ability do very well just by being tenacious and willing to die 50 times in a race.
Have fun...go fast.