This one is a long time coming there have been several theories that can be reason he is still10. I figure we can start numbering theories. which one you preferred.
- Time control Pokemon theory: there are few pokemon with the ability to control time. those incded so far are celebi and dialga
- Ash coma theory: this is popular theory stating that he was in coma after the explosion.
- Different planet rules: as joshmightbe mention in another thread that they are in Jupiter. With the environment that is possibility
- Lazy writing and no way out of it: if want to take the lazy way out and can not think of a clever solotion
- The pokemon world is Neverland: they have pirates (team aqua) living shadows (gengar), fairies (clefairy) and they have crocodiles that will constantly chase you (Krookodile)