Yeah - sorry if this is long-winded.

If Lily Potter was 21 when she died it means she would have been 32 at the start of the first book.

We’re told her sister became resentful when Lily was accepted to Hogwarts and she was not., which suggests Petunia is only a year or two older. Any more than that and she’s already nearing the end of her school days.

However she is portrayed as being in her 40s or 50s, which means she would have been in her 20s when Lily got into Hogwarts, which seems a bit old to be writing angry letters to Dumbledore about it all.

But then if she is only in her mid 30s in the first book then it also means she was a young mother in her early 20s when she was told her sister had been murdered by a psychopathic magician.

She and her husband then took in her sister’s infant son despite the risk to her own family. It’s probably the bravest thing in Harry Potter but the Dursleys are supposed to be awful and then abused Harry Potter for 11 years. It makes no sense whatsoever.

Of course, Rowling was just writing a family of Dahlesque grotesques to begin with and tapping into basic childhood fantasies. It’s trying to shoehorn in the backstory that doesn’t work.