I like this reading of Thor being relatively young, because if he is young now; then it makes sense for King Thor to exist especially since Odin himself is over 1,000,000 years old as seen in Avengers One Million (please don't debate with me on the merits of the timeline that Aaron has set up).
Thor's age also has to do a lot with his brash and impatient self and the fact he doesn't really have an identity beyond the wielder of Mjolnir and it isn't until War of The Realms does he finally get his identity.
For me whenever there is a new writer I always take it as a soft reboot; for ardent continuity fans, I say this is a fools folly; because it's not possible and it doesn't matter how much mental gymnastics you do.
Sure Ragnarok happened, Odin is strong man, Thor is a unflinching god man that MRA's can look up to... until he isn't.
I can imagine a ton of Aaron fans will be upset with Cates when he decides to change things up, but alas this is the nature of the medium.