as I recall ho-oh was the first legendary we see in the anime but nothing big has ever happened with it yet right? it hasn't played a role in any movie, it just kind've appears then disappears, is it supposed to be symbolic?
" The rare few who bear witness to Ho-Oh are promised an eternal happiness. "
Ash saw Ho-oh and he got eternal happiness. For him to be happy forever is to be a Pokemon trainer for ever. Its probally why he is 10 forever too. Hope I helped! :D