David and Kathryn did not spend X years growing up, meeting, dating, falling in love, getting married and having marital problems. From the very moment Storybrooke was conjured up, Kathryn has only ever been a woman who thought her husband left her. That is who she has been from the second the curse created Storybrooke. There is no marriage, just as there was no falling out. They were never together for a second. The curse created false identities for the real people (Prince James Charming and his former intended) and part of those false identities are these false memories.
For that matter, Regina never found David unconscious. David started out in a coma. Queenie's curse created that story, too. The real man, Prince James Charming (I know Charming isn't his last name, but I just want to be clear about who I mean), was stabbed, while still living in his real world. As a result of his wound, James lost consciousness. The curse overcame him, his wife, and everyone else in the Enchanted Forest, and created this false reality, with false identities, false memories, false circumstances.
The Henry Problem: Assuming we can believe what we have heard, then Henry was born in Phoenix, and was born outside of the curse. If this is so, then when he is transported to Storybrooke, he ages, while the rest of the residents don't. He is subject to time. The Enchanted Forestians living in Storybrooke still are not (or were not, until Emma came to town), even though they were coexisting in the same space with Henry. Think about The Narnia Chronicles, for a moment. Sometimes, the Pevensie children will return to England after having spent years in Narnia, but only minutes will have passed (in England time). Sometimes they will return to Narnia, after having passed only a school term or whatever in England, and centuries will have passed in Narnia. The time difference is never the same. There's no way to convert England units of time to Narnia units of time. There's no way to track the changes. The two universes operate under different rules. (And in the end, it turns out that Narnia is the only real place.)