Limping AA is really not a great idea most of the time, particularly from UTG. Reason being, you're devaluing the strength of your hand. The results will be either reduced equity with a lot of callers, or in this situation: reduced maximum value.
Your UTG +1 raised to $7. In a live game that's generally indicative of a speculative hand +value. 66, 77, 88 (speculating on hitting a set), TJs, JQs, KQs, or A-Rag suited. From early position, A-Rag suited is most likely, but sometimes people will min raise pre-flop with other speculative hands. Logic here is that they can cheaply inflate the pot against multiple players and then get exponentially more value post flop. I'm of the opinion that this isn't a great play from early position, but people do it.
Everyone else limped simply for the fact that there's now decent pot odds
. Every J8 and Q7 is coming along for the ride.
Now you're in a situation where if you raise too low you're against a huge range of cards and going to the flop out of position. So that's no good. And if you raise too high, everyone folds out. Unfortunately, there isn't much middle ground here, so overall your best option is to raise big and take the pot down. That's ok, $40 ain't bad.
Now if you opened $10-$14 (depending on the table) you're much more likely to get only one or two callers, and maybe a couple streets of value.