Last night I was researching if there were references outside the anime to Misty's parents just because I find it curious since she's one of few series leads whose parents never made at least one appearance and came across quite a bit of startling revelations of how sexualized she is in Japan despite being established as 10, the same age as Ash.
(Side note: I did find an answer about her parents. It seems they're referenced in a canon graphic novel depiction of the anime. Apparently, they couldn't handle the strict gym regulations so they ran off and abandoned their daughters).
Starting with the entire reason her character was created which was to attract more of a male audience which is laid on rather thick if you think about it.
She's rather endowed for a child, is depicted in more than one instance in revealing outfits such as her mermaid costume for her gym performances and there is an old ambiguous Japanese Pokemon card that has her silhouetted as swimming perceptively naked with Starmie.
Worst of all, she's been ogled by older men.
ex. 1 In the Japanese 'Beauty and the Beach' an elderly man tells Misty that he's looking forward to her becoming legal age. For obvious reasons the English dub changed the line so that he just tells her she reminds him of his granddaughter.
ex. 2 Alright admittedly I don't remember what episode it was, but I distinctly remember an episode in which Pikachu becomes ill after eating an apple or something (I think it turned out he'd just eaten too fast and swallowed a seed or something), there is no Pokemon Center in the area so the group has to rush him to a human doctor and the doctor immediately fawned over Misty, even calling her cute.
We can also examine Brock. I recently found out in a reddit post that he's 15 rather than 18 as I had assumed and he was at one time the sole guardian of his younger siblings.
If you really think about the entire concept of Pokemon, children are allowed to leave home on their own to interact with potentially dangerous wild creatures at the age of 10.
So, I believe it is safe to say that it is established Pokemon universe culture for 10 to be considered an adult age and might not be far from real Japanese/Asian culture. There is a documentary on I believe Netflix which follows Asian children as young as 4 or 5 being sent out on errands alone if I am correct.
