conjunctions - until VS. before

When you are to choose between two conjunctions, ˜until' and ˜before" for the following sentences, which is more natural?

1. Most children do not start school ( until, before) they are six years old.


2. 
   

   Jake live in N.Y. (until, before) he was thirty years old, and then he went to LA.

   
   

   To me, ˜until' sounds better for both sentences, but ˜before' doesn't sound bad either. Any comments would be appreciated.

   
   

   Sentence 1, which has a negative verb, is natural with either form. "BEFORE they are six years old" implies that they do not start at any point in time before their sixth birthdays. "UNTIL they are six years old" states a condition "” "be six years old" "” that must be fulfilled. Either statement is OK.

   
   

   Sentence 2 is a bit more complicated. If Jake lived in N.Y. UNTIL he was thirty years old, he went to L.A. as soon as he turned thirty. If you say only "Jake lived in N.Y. BEFORE he was thirty," technically Jake could have lived in New York and in many other places before he was thirty. You could say "Jake lived in Stockholm, Beijing, Istanbul, and New York before he was thirty." But this sentence makes it clear that there was no time interval between his living in New York and his going to L.A., because it states "...and THEN he went to L.A." Apple's sentence is therefore unambiguous with BEFORE because of the adverbial clause "THEN he went to L.A."

   
   

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One of my friends has provided the explanations. I am, however, confused with the bold parts, that is, does the preposition "until" make a condition??

What is more, I failed to get the bold parts at all.