Humans have been able to live in the woods and thrive for thousands of years.. If his father knew what he was doing there is no reason for them to starve.
Yes.
Which means, if they had the ability to survive well, for five years in the woods, that kids should still be able to survive well because he’s had 5 years of training.
People are consistent. If they hate society enough that they’d rather be in the woods, it doesn’t seem likely that their first concern for their child is to seek civilization upon their death. They’d probably work overtime to give their child survival skills so they wouldn’t have join society.
The use of language also degrades quickly, if it’s not constantly used. If this child really spent 5 years of prime development time in solitude and away from having to communicate, his language skills should be much more primitive than his age.