STOP! The following article contains a discussion of details in the Supergirl pilot episode which may be considered SPOILERS. If you haven't seen it, and don't want to know details, please don't read any further. Any SPOILERS are minimal and focus only on the character of Jimmy Olsen and not the actual plot of the episode.
When Mechad Brooks was first cast as Jimmy Olsen in CBS' Supergirl, the fan base was split over the color of the actor's skin. In the comics, Jimmy Olsen has traditionally been a freckle-faced, fair skinned ginger, and Brooks doesn't exactly fit that persona. However, when the first trailer for Supergirl was released, and the full pilot episode was leaked shortly thereafter, the controversy began to take on a completely different tone. Yes, there were still fans out there mad because Brooks was black, but now they had shifted their outrage to the fact that Brooks was playing the usually semi-geeky character as decidedly confident and mature. On the surface, this might very well seem like a valid criticism, but I think that there is something fans are completely missing.
First of all, many traditional Jimmy Olsen elements are present. He is a photographer, he is described as being Superman's pal, and he even won a Pulitzer Prize for his first photo of Superman. When you look past his race, he is still recognizable as Jimmy Olsen. Now, I am not going to say that everyone who is hating on Brooks' portrayal of Olsen are hating based solely on race, because I don't believe that's true. I'm just stating a fact that if you forget he's black, he does resemble the comic book Jimmy Olsen in many ways. There are certainly some distinct differences, to be sure. Big ones, in many cases. First and foremost, Brooks' Jimmy Olsen, who prefers to be called James by everyone except his mother and Superman, is a very strong and confident character. He's charming and definitely presents himself as his own man, and not just Superman's honorary sidekick. This is definitely a departure from any version of the character ever portrayed in any medium before. However, I think there is a little more to it than just simply a new interpretation.
When Kara left Krypton shortly before its destruction, she was 13 years old. When she landed on Earth, she was still 13 years old, however due to her ship being trapped in the Phantom Zone for a bit, Superman was already grown up and Supermaning when she arrived. This means that, since she is between 23 and 24 in the show, Superman has been flying around Metropolis for at least 10 years. We don't know how long he was Superman before he discovered Kara's ship and left her in the care of the Danvers family, so it could actually be longer than that. Now, in most iterations of the character, Jimmy Olsen is there from the beginning. He is interning at the Daily Planet and taking pictures before Clark Kent even gets a job there. So we can assume that Jimmy has been present and has known Clark/Superman for the entire 10 years - or longer - he's been around.
The point is, Jimmy has probably done a lot of developing and maturing as a person in the 10 years that he's been hanging around Superman, and presumably forging strong relationships with Clark Kent and Perry White as well. Perry White has always been something of a mentor to Jimmy, and in Lois and Clark: The New Adventures of Superman, Perry had a strong hand in guiding Jimmy (both of them) into manhood. We also saw Clark Kent, acting like somewhat of an older brother, encouraging Jimmy to be more courageous and more outgoing, helping him to better talk to girls and to stand up to Mr. White when he feels he's been wronged or otherwise treated unfairly. There is no reason not to assume that Brooks' Jimmy Olsen has had similar experiences with Superman, Perry White and Clark Kent. He's had strong male figures that have spent the past 10 years guiding him into the man we see in the Supergirl pilot.
Yes, the Jimmy Olsen played by Mechad Brooks is very much his own man, forging his own destiny, he even says in dialogue that Superman sent him to National City to watch over Kara because Superman knew that Jimmy was wanting to go out there and build a life of his own, and make his own mark in the photojournalism world, out of the shadows of Lois Lane and Clark Kent. Yes, this Jimmy is much different than the Jimmy we have known, but that is because he is Jimmy Olsen in a time period of his life that we've never seen before. We know and are used to Jimmy the kid, the intern, the sidekick. That isn't Brooks' character. His character is Jimmy the man, the full fledged reporter, no longer just a cub. And he is no longer the sidekick. In a lot of ways he is now the mentor, because he has spent the past 10 years being mentored by Superman, and he is probably the best person, aside from Superman himself, to help guide Kara as her cousin once guided him. So step back, look at this new Jimmy in the context of the story he's in and not in the context of the stories you've known. Those stories are in the past, and they have all served to help develop him into the character we now see in Supergirl, truly a Jimmy Olsen for the 21st Century.