I too saw the original Star Wars trilogy as a child; I was seven when Episode IV: A New Hope came out. I saw The Last Jedi last night, and was very glad I didn’t read any spoilers or reviews of the film first, so I came in with few preconceptions.
I was neither surprised nor disappointed by Luke Skywalker’s actions in this film. I like characters in fantasy stories to be complex, not one-dimensional. I never had the idea that Skywalker was a flawless person. The idea that the Jedi religion, the Dark Side, and the Force represent a binary choice between good and evil is overly simplistic. As a child the added nuance in this film compared to earlier entries in the series might have been lost on me, but in middle age I can appreciate that complexity.
Though he displays human flaws, Skywalker, along with the other principle characters, is arguably not human; this story takes place “long ago, in a galaxy far away”, and its characters should not be held to our human concepts of morality or religion. People criticizing the racial diversity of the modern films’ casts ought to keep the fantasy setting in mind as well, instead of assuming any humanoid who isn’t CGI-generated (or Lando Calrissian) should naturally be white.
I suppose as an atheist the idea of perfect redemption doesn’t work for me either. When Skywalker died, my take was that it was of exhaustion from his force projection efforts; it wasn’t until Rey spoke of his “peace and purpose” that I could appreciate the symbolism of his final actions and absorption into the Force. The Force seems more like a Buddhist than Christian concept to me, without any theistic entity making decisions on who is good or evil, worthy or unworthy. But Buddhism (in the Theravada tradition I studied for a brief time, at least) still has the binary concept of enlightenment — you are trapped in the cycle of death and rebirth until you ultimately transcend it for Nirvana— which is part of what drew me away from identifying with that, or any other, religion.
In real life, I don’t believe any individual person is good or evil, and try not to describe people as such. I believe that individuals make choices and perform actions that cause more or less harm, and we should all strive to cause as little harm as possible to each other, our fellow animals, and our natural environment. (The Last Jedi had some nice messages about animal liberation in that regard, but that’s for another story.) Regardless, again, Star Wars takes place in a fantasy setting, and the characters are not subject to our world’s morals or rules, including the idea that heroes should be flawless.