User blog comment:Sargenttacos115/Why are Sting and Rouge so weak?/@comment-117.227.194.37-20131110013056/@comment-24039250-20131114005245

Also when you think about it how old were they when they killed their parents? Sting and Rogue are 19 now, so 14 years ago on 7/7/X777 when the dragons disappeared and when they killed their parents they were only 5 years old. The only type of experience they probably had were the knowledge of magic given to them by their dragons and maybe some basics in fighting. Since one was on their deathbed and the other was old and was asking to be killed, it was simple to kill them even with their age. This would give the two dragon slayers 14 years to grow and train themselves to become what they are now.

With Rogue it took him seeing Gajeel in Phantom Lord to strive to become someone as great as him, prompting him to train and that was likely 7-10 years ago (idk when its not specified when Gajeel joined PL or when Rogue got obsessed with him).

With Sting, its clear that at some point in time after Natsu was begining to make a name for himself in FT, Sting became inspired to become stronger than him and to prove to everyone that he is a true dragon slayer (also there is that promise with Lector that keeps him going). I'm going to say that it was 7-10 years ago when the two started on their goals to become strong, and it was also revealed that Sabertooth didn't become the Best Guild until a few years before FT returned from their Timeskip since they say "during the timeskip" not 3 seconds after they disappeared Sabertooth became the strongest. Sting and Rogue likely joined the guild around 2-3 years ago and with Natsu and Gajeel not around slacked off a bit in their training since their drive to become strong was gone.

Natsu and Gajeel were always training even from 14 years ago, especially Natsu since he is always trying to prove how strong he is. Natsu and Gajeel have more experience in battle and if I had to sum up their powers, I'd say that without the 2 moth training for Gajeel and without the second origin for Natsu they would have lost for sure or they may have won with great difficulty (meaning that both would be on the verge of collapse at the end of the battle and it may have been called a draw).

In the end Sting and Rogue are NOT weak, but are just not as experienced as Natsu and Gajeel are. Though I will say that the only reason they are at the level they are at now is because of the implanted lacrama they have in addiction to their power which gives them Dragon Force. If it wasn't for that they would be considered weak for sure to the point of losing to Elfman pre-timeskip. If Natsu and Gajeel had a lacrama implant in them now, they would be insanely strong (maybe near/at Gildarts level....naww thats crazy).

Sorry for the very long response.