How Do You Carry?

I keep having these games where ill be like 6/0 or 7/0 at the ten minute mark, but then we still end up losing the game (usually because our team doesnt group at all or listen). So how am i supposed to carry to win? I went 6/0 last game before the 10 minute mark as Nocturne Mid Lane. Then every lane i went to, the enemy champ would just back to their base, or, if theyre a trist/gnar/kass (all 3 of those were in the game), they could basically just fly away when I engaged. After 5 minutes of not being able to get a kill off this, I just go back to my lane to freeze lane and farm cs. Then thats when Rengar camped me, basically deleting me in a few seconds. I took all 6 outer towers down (couldnt get the inhib towers due to how hard they protected it), and then after that, the team basically didnt want to group thus we lost. Olaf kept getting caught, they got baron, they ended. So how am I supposed to carry? Ive been practicing over and over on my Silver 2 alt to try to carry in ranked, but I can never seem to do it mid/late game.