Can I apply at any time?

No, you do not have to apply prior to turning 31. If you qualify you are eligible to apply.

Why is my case taken almost 20 months without an answer ?

My colleagues both make good points. There is also the likely possibility that there is an issue with your case and that an RFE will be issued...

Is there any way to waive the filing fees because USCIS rejected my old version N400 and still processed the paycheck?

Wait until you get the receipt notice for your case. Log into your bank account and look at the scanned copy, your receipt number is usually...

Do I have to pay the filing fee again if I have submitted the old N400 on May 14,2014?

You are not going to have to repay, don't worry.

Is it normal for my deferred action case to be under initial review from October 22, 2012 to May 23, 2014?

Unfortunately there are some case that are stuck. We have had some outlying cases pending from 2012 and have done everything your attorney has done...

Do I have to file a provisional waiver?

Based on the facts presented no 601A is required.

Applying Deferred Action for Childhood Arrivals after expired F1/OPT visa.

Yes, if you meet all the requirements, the fact that you previously held an EAD has no bearing on your case.

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On the G-325A when I check other what do I put?

Status as permanent resident is what you will mark. The K-3 is unlikely to speed anything up. Currently they are processing at about the same pace....

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Change of Status

No, you cannot change status from a green card holder to a non-immigrant.

I was born In India but my Wife was BORN in BAHRAIN ( India passport though)

Yes, based on your facts you could benefit from cross-chargeability. Contact an experienced immigration lawyer that is familiar with how to proceed.