no insult on you, I just wanted you to see the math so you knew why I suggested what I said:
turned 15
Christmas
Participated in Hoenn League (I don't know much about this, but assuming that it's official, there would be a registration phase, and there would be several weeks of different things taking place)
^1 year?
Travel to Sinnoh, participate in league - make it to Final 8 (once again, if he wasn't KO'd in round 1, then there would be considerable amounts of time between battles, trainers wanting to take rests, and there only being a small number of battlegrounds available)
^another year?
Travel to Unova, Participate in league (see above)
^another year?
travel to Orre
^another month
In Orre for 3 months
^+3 months
now, that means that it's before Christmas two years later, assuming that your Character's Birthday is very close to Christmas. - I normally put in the rule of 1 year per league - considering you would have to beat all 8 Gyms again. Really, your character would need to be 17/18, or have left earlier. It's a big world, and you don't always win every battle with ease like in the games...
also, if he is using some method of transport (remember, it's impossible to use Fly or Surf between Regions) - you would have to buy tickets, Book ahead (he didn't plan to go to sinnoh before the league, did he?) and then boat trips would take weeks (if it's a plane then it would take maybe a day max, but you don't see too many planes in Pokemon)
I'm sorry if I come across as rude, but I just feel that the massively short time of your travels makes your character really Mary-sueish (remember, Ash left when he was 10, and he is what? 15 now in Sinnoh? remembering that Johto and Kanto are litterally next to each other)