I can too easily and repetitively. am i normal?

hi im nearly 13. i can reach a within 25 seconds and i can then continue repetitively. the first fells quite good but then they arnt as good. i started masturbating at 9 and at that age it would take me a couple of minutes to reach s and they would be great but then i suddenly get these strange . what is wrong with me. I really dont want to go to the doctors and tell my parents. Thanks in advance,