Im prior service Navy and in the process of doing the Blue to Green program. I was talking to my recruiter about going to 68W school but with a M6 designator he told me that it be better if I returned to my reserve unit upon completion of WTC and AIT that I request it there and that Id have a better chance of getting it rather than going to MEPS and getting it in my contract. I was wondering if there was any truth behind his statement?

M6 is not for enlistment any longer. You must be a 68W for 12 months or so before you can get this identifier.

So the recruiter was telling the truth then... Is there a specific rank requirement that they cut off your elgibility to get that designator?

This ASI is for SGT and below.

Here's all the information you'll need for M6 ASI:
http://appd.amedd.army.mil/Enl_pg/Enlisted%20WebPages/91WM6%20ASI.htm