My first time masturbating was when i was 13 years old. after the first time i masturbated i for some reason can't last long masturbating any more. its been 7 years and i can only last about two minutes every time. why can't i last long masturbating?

What you described is normal. You may try using a water based lubricant like K-Y jelly and reduce the pressure on the penile head when masturbating. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.

Pl do not start timing as ejaculation depends on a lot of factors. Once you are sexually active and comfortable with a partner you will be fine.