Look at the level kakashi and itachi were at when they were 12 and 13 and compare it to naruto and his class. The strongest was neji and he was only low chunin level. Why do you think shinobi developed faster in the past?
Because they grew up in more dangerous times than Naruto and Sasuke did in their early years. There were wars happening before so ninjas had to be more hardcore growing up otherwise, they wouldn't live to see tomorrow.
Obito/Rin progressed at normal rates (or maybe slightly above average). They were chunin at 13. I think it can be assumed that the rest of that class of shinobi were chunin at that point as well since Obito was like Naruto without plot support back then. Kakashi was just special.
And I thought it was made very clear how talented Itachi was compared to pretty much everyone during his childhood.