I'm 17, weight a little under 130 and 5'8". I plan on doing ab workouts and pushups every day and running 2-3 miles at least 5 times a week. My BMI is about 19.5. My stomach is pretty flat but there's no definition to my abs yet. Do you guys have any ideas for ab workouts and do you know how long it'll take me to get a 6 pack?