I guess it's a good thing the Rams didn't think about "steps" when they hired Sean McVay at age 30.
Ummmm, Sean McVay started coaching at the NFL level in 2008 as Assistant WR Coach in TB under Jon Gruden.
Then he spent 4 years as a TE coach for the WFT under Mike Shanahan, before getting promoted to OC for 3 more years under Jay Gruden.
So while McVay was a really young HC, he had 8 years of NFL coaching experience (and not including his 1 year coaching in the UFL) before he got his shot at HC.
Kellen, on the other hand, has just over 3 years of ANY coaching experience (1 as QB coach, 2 as OC).
So while I am not in the camp that a coach should have 20+ years experience before one should get a shot at HC, I believe making Kellen the HC at this point of his career reeks of Jason Garrett rather than mirror Sean McVay.
IMO Kellen is on his way, but the beginning of this year has been the first year I have been impressed by him as an OC. His first two gameplans this year have been spot on. He still gets a little too cute at times during the game, but he's well on his way even if he isn't ready .... just yet.