Brock is 15 as per official material. Ash is short even for 10 (several boys his own age are taller than him, Gary for instance). Misty is a bit of an early bloomer (but not as much as her ecchi fanart would have you believe!) and is a bit tall for 10, making her height compared to Ash look really exaggerated early on, which is why so many people mistook her for being a teenager herself (and bumped Brock up to late teens), but she is firmly 10 as well.
The Rockets ages are less clear cut than the kids. But I strongly believe Jessie and James are in their 20s. Firstly, the "17-years-old" thing comes from a single scene where (and I'm quoting here
>>49392270), in the original, Musashi listed her age as 17 and her profession as "idol". I don't think a single nip took this as anything other than her obviously bullshitting.
The dub translated this as Jessie writing her age as 17 and her profession as "super model"
Since this was the only ""official"" source for her age for a while, people took Jessie - the character - at her word (kek) and started citing this scene as proof that Jessie and James are 17. Whereas in context it's clear that Jessie is bullshitting and trying to pass off as younger and hotter than she really is.
Finally, and again I'm quoting here:
> ... if you want something more official, Miyamoto, Mushashi's mother, wrote the Mew report shortly before she died, 20 years before M1, leaving an orphaned Musashi of indeterminate age. But I estimate a similar age to Eureka, Hoshi, or Suiren's twin sisters.>Next is from bulbapedia, but I can't confirm it, I haven't seen that movie in Japanese:>In the Japanese version of The Power of One, Jessie tells Ash and Misty, who are 10 years old, that they're 10 years too young to talk about love, and James adds that he and Jessie are five years older than that.That last bit would ping their ages at exactly 25 which to me sounds about right.
