Alright, so I've been thinking about the timeline of the main series in relation to this story. I've decided to alter some of the ages of the characters, so I figured that I'd lay that all out in one document and update it as and when things change with the story.

Start of the Story:

I've decided to make Ash 13 in this story. My reasoning for this is as follows:

- I envision Ash's Kanto Arc and most (if not all of the Orange Islands Arc) to take a year. There's 116 episodes in those two arcs combined, and obviously not all of these singular episodes took place in the span of one day (as witnessed through the episodes). If you also take into account the travel time between cities and such, I believe a year is a could estimation. This places him at 11 when the Johto League arc starts.

- I believe that Ash's Johto arc would've probably taken about 10 months. Though this arc has more episodes than the previous arcs combined, Ash would've been a more experienced trainer at this point, which is why I think it would've taken him slightly less time to travel around Johto than the previous regions/areas. This places at him being a couple months out from turning 12 when the Hoenn arc starts.

- The Hoenn arc has 131 episodes. I've always figured that the League Conferences must occur in succession to one another, because if all the conferences occurred at the same time every year, then characters like Charles Goodshow wouldn't be able to appear at them all (which he does up until Gen 4). I've placed the Indigo Conference in late April due to the fact that it's been thought that Ash got his first Pokemon in April, meaning that if a year passes on his Kanto journey, he'd be just in time to compete. I've placed the Silver Conference in early June, due to my timeline of his journey in Johto taking 10 months.

Due to it being shorter than the Johto arc in terms of episodes, I've placed Ash's Hoenn journey at 9 months, which places the Ever Grande Conference in March, by which time Ash would've turned 12 and would be about 5 months out from turning 13.

- The Battle Frontier Arc only has about 60 episodes, which I think would be perfect to fill that 5 month void between him turning 13.

For these reasons, I place Ash at 13 at the start of this story.

I've decided to place Dawn at 12 in this story. I know that canonically that doesn't make the most sense, but I felt that it would be odd to place her at 10 whilst I age everyone else up. Furthermore, placing her at a year younger than Ash makes sense from an experience standpoint, which we have seen be reflected in the anime through the relationship between the two characters in how Ash acts as a pseudo mentor to our favorite Coordinator.

I've placed Brock at 18 in the story. His canonical age is 15, so as I have aged Ash by 3 years, I figured it would be best to do the same to Brock.

Now, when it comes to Casey's age, I have decided to place her at 15.

I reckon she would've started her journey at 12 instead of 10, simply because she would've wanted to learn more from her Grandpa before heading off. Plus, she would've assisted in raising Monferno when he hatched as a Chimchar, and I suspect she would've prolonged her stay in the hope that he might've been able to come with her (which, as we know, it couldn't at first).

She previously had travelled through Kanto and Johto, but the difference with her journeys is that she took them alone. This, coupled with the fact that it was uncharted territory for her, would've made her journeys take longer than Ash and Brock's.

Her Johto journey was the one she took first, which would've taken her about 13 months (which is plausible since she would've started about a month and a half before that years Silver Conference, and therefore would've made the one the following year). This places her at 13 by the time she starts her Kanto journey.

I believe her Kanto journey would've also taken her just over a year (during which time she would've turned 14), which means that she would've missed the next Indigo Conference that would've occurred in April. Due to this, I believe she would've taken some respite from the end of her Kanto Journey (about July) to the next Indigo Conference (the following year) in order to train and be ready.

9 months later, she would've competed in the Indigo Conference before heading back to Sinnoh, where she would've gone back home for a while before setting off again on her next journey in her home region, and during that layover time she would've turned 15, placing her at her starting age of 15 at the start of the story.

End of the Story:

Don't worry, we're nowhere near this point yet, but I thought that I'd clarify the length of the Sinnoh journey and what the character's ages will be at the end. There's 191 episodes in the Sinnoh arc, but quite a few of them are double episodes or occur in direct succession, so I reckon that the story's event occur over about 8 months. Unorthodox, I know, but please just go with it XD. Logically, this places all the characters at about a year older than they were at the start of the story by the end.

Therefore, the character's ages will be:

Casey - 15 (nearing 16)

Ash - 14

Dawn - 13

Brock - 19

Sequels?

Yes, I do intend on writing sequels. I have decided that I will be skipping the Unova arc for Casey, but I do have something planned that will fill that void for her story wise whilst Ash is in Unova. I believe Ash's Unova journey took about 7 months, because lets be real in saying that the Decalore Islands arc couldn't have taken that long at all.

That will place Ash at 14 still heading into Kalos, whilst Casey will now by 16. I've decided to make both Serena and Clemont 14 like Ash, but I have chosen to keep Bonnie at the age of 8 as she seems to be canonically, simply because if I aged her up by the same amount as I have as the other characters, she'll be an eligible trainer herself and her role wouldn't make much sense.