I’m all for this theory!
BUT…instead of an alternate universe, I think Regina and Robin actually met in the tavern, fell in love, ran off, married, and started a family hence Lily. However, because of a certain event, you know the first thing to come to a King’s mind about his wife disappearing, and seen by a well known thief would be that Robin kidnapped Regina, thus putting his life in danger. Knowing that too much was at stake, Regina went back to Rumplestilskin or probably met the Sorcerer himself to do what Gerta did, erase the entire realm’s memories of the event. Hence altering the original course of the book, which is how we got two different pages. And then Regina gave Lillian to the Sorcerer to give her daughter her best chance, and the Sorcerer sent young Lillian to this world, with the star mark so that one day Regina would know her daughter just as she knew her soul mate by the lion tattoo.
The Age Issue doesn’t really matter…Ingrid was forty when she was unsealed out of the Urn, and came to this world before the curse was even cast. 34 years later, and Ingrid still looks like she’s still in her forties. Perhaps it’s the Sorcerer’s magic that keeps them frozen in time until their mission begins. Lillian’s mission…one day restore her mother’s happy ending.
"If you go as far as you can see...you will then see enough to go even further." - Finn Balor