Understandable. I am not sure if the original trilogy can have the same impact on people if you watch the first time when you're older (I am sure, it can't). I think the real magic happens when you see it as a kid, maybe 7-11 years old. Still you could give New Hope a chance, the originals are different from the crap they made later.
I was older when I first saw the original releases at the time of their release 1978 for the first one (yes 1977, but didn't get to my small town until 1978). Two things made the movie have impact. A simplified almost fairy tale heroes journey, and what were then the first "great" special effects that didn't detract from the movie. So it helped with the suspension of disbelief to put you into a Galaxy far, far way a long time ago. The special effects from these will in no way Wow! your daughter in today's world.
So my first answer was 1977 original release, but thinking on it more, maybe Rogue One first. You'll have to decied. Rogue One is a dark movie for some 12 year olds, and the originals managed to avoid such darkness despite being about worlds destroyed by evil masters.
I consider the three pre-quels a money grubbing stain on the franchise. Only Revenge of the Sith would I consider good. Other than Rogue one, those after it are just updating retellings of the same tale and faint echoes of the original.
I do like the fun loving Solo: a Star Wars story.
In the prequels you'd think Lucas forgot how to write and how to direct. His work is appalling in these. Makes one wonder if his 1st wife, who was a great film editor, and had input into key scenes in the original 3 Star Wars movies didn't have more important input than is realized. She was not part of the later movies having divorced him.