I only smoked marijuana 4 times in my life ( i was 16 when i smoked it). will this have an effect on my health in the future ?

Unlikely: If you don't smoke anything now or in the future your lungs will self clean any debris left behind & you should be fine.

Agree with Dr. F: Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV vaccine. Wish you good health!