You guys are aware he is playing Multiplayer and not Immortal/Diety right? In over a hundred games of MP I have never seen GL before turn 35 and many times it's left until turn 75+ because nobody wants to "risk" going for it and losing it 3 turns before completion. So like I said, if playing Babylon then rush it, otherwise ignore it. In MP if someone gets GL between 35-40 chances are they are Babylon or Korea and went for it for the mid-late game GS spawns. Which means they are going SV or tech-lead Domination.
EDIT: Also it's never a bad thing to "steal" a wonder out from under someone since all that production is basically lost and they are set seriously behind.