The 2 brews he tasted these in fermented between 64 and 68 degrees both were Wyeast 1056. I'm not thinking that the temp was an issue.
I've gone back through and tasted the beers myself and I don't pick up this plastic taste but my friend pointed to the Chlorophenol taste on this link as a comparison.
I felt at first that it would be the water as I don't taste the plastic, but given that it seems to worsen with age I thought it might be an infection. Would a chlorine water issue worsen over time or fade out?