I have to say something about how to approach fiction, because while I think I've always done it automatically, judging by online discourse this is not universal: when engaging with fiction you should just accept the premise and in-universe rules.
For example, you reading a story set in the past and the main couple are 17 and 25. Does everyone in the story treat this as a totally normal age gap? Okay, then for now, put your 21st century morality in a little box and label it "real world morals" and then put this couple's age gap being normal in a box called "in-universe/historical morals" and accept that you can store both boxes in your mind without exploding because you are are thinking, rational human being. Because it's driving me straight up a wall that people can't seem to do this!
"He kills people, what a red flag!"
"Ma'am, that is a magical warlord and if he stopped killing people they would kill him. He doesn't have an office job."
"That was very dubious consent. I can't support this ship."
"Sir, she grew up in literal hell, I doubt they had comprehensive sex ed there. Also, she might learn and grow?"
"She's only sixteen, he's a pedo!"
"If society at that time says that sixteen is the marriageable age, then no, he's not. That is not how any of this works."
"They grew up together and their parents want them to marry? Gross."
"Yeah, it would be weird today, but everyone is treating this as normal. I guess it was A Thing."
Sure, in a modern, non-fantasy story set in your country, judge by your moral code all you want, but if you want to actually enjoy a story that isn't written with your exact morals, you need to accept the premise. Step back later and do some analysis, think about how society has changed (hopefully for the better), but keep in the mind the intent of the author in that time, culture, genre, or universe.
Yeah, Marianne Dashwood & John Willoughby are a creepy age gap today, but Jane Austen thought it was normal so while you read Sense & Sensibility, you can do that too. I promise it will make your reading experience 1000% better and you won't go straight to hell or anything. If you can't handle that, I banish you to the non-fiction section of the library.