For Odd:

He was very inquisitive and polite as a young boy (albeit a bit socially awkward), but around age 13 he was a bit more privy to some of the scarier/mind-bending stuff to his past and the circumstances around him, so around that time, so he tried to cover up his increasing mindset of "My god, what is happening?" with a veneer of humor (with varying degrees of success)

By around age 17-18, when his father died: He did NOT take it well. By this point, he had already taken on some of the responsibilities his connection to Giratina came with, but he grew a bit more spiteful and vindictive in his practices: never intentionally trying to hurt anyone ((most of the time)), but certainly more callused and careless with both his words and his actions.

And then a year or so after that, with a lot of things in his story coming to a head (in a rather unfortunate way), Odd was left pretty shell-shocked in the aftermath and decided to get away from it all for some DEEP reflection, hence why he's hole'd up in his shop. Nowadays, he's much more mellow and used to the strange stuff that happens to him, but he's still sifting through a lot of baggage