Just go for it and enjoy them fresh! They taste the same to me! But I'm no expert!

Concur, the only reason to wait until maturity, is that they can be stored for a period of time depending on the cultivar. Green onions need to be used immediately.

Tagging along on this...

I know that some say that when your onions start to lay down by themselves, you can just bend over the tops of the rest. But is there any problem with lifting the onions at this point and starting the drying process (under cover)without waiting for the onions to dry in the field?

The maximum growth stage is when the onion plants start to bend over. as long as the leaves are good the onion is immature.

I planted first multiplying onion in the Spring of 2011 & harvest in June(catalog said too). But this year my onions are still standing tall, so I am going to wait till the tops fall over.
But I want to see how long they will store.

Thanks, everyone! I have a few that are starting to get to a decent size, so I'll probably start eating fresh onions any day now.