What about when Red Leader calls out to him in the hangar. "Skywalker! Can you handle this ship?" Or something like that...
Portman was 16 when they were shooting TPM. They filmed in 1997, she was born in 1981. Christensen is actually only a few month older than Portman though for when they filmed the rest of the movies.
That's ridiculous. Luke had a father. Besides, I know of no authoritative source which says that "no father" was in the prophecy. And if we're defining Chosen One status by having a hand in the outcome, then all those who helped out along the way are collectively the Chosen One and that's obviously a non-starter.