What am i supposed to do???How young is to young?

I have a friend, he is a known liar throughout the school. He just told me that he had . We are both 15. Is that too young? What am i supposed to do about this? I wish he didn't tell me this. I feel like i have to tell his parents (who my parents are close with). I can tell when someone is lying, he isn't. If i tell his parents I'll be known as the biggest snitch in the school and he will hate me forever. Is it bad if i dont say anything? (i am not the only one of his friends who knows) Underline Question...WHAT AM I SUPPOSED TO DO!!!!????