How much is 168lbs hurting Glen Johnson?

I just caught a clip of Johnson v A Green and have to say i think boiling down to 168 is gonna prove a big mistake for the road warrior, i know he fought for years at 160 but has been at light heavy since 2001, ten years, and boxed as high as 180lbs in 2008. At 42 years of age to drag your old ass back down to super middle is going to be detramental especially against a strong fighter like Froch. Too many fighters messing with their weight and not learning from mistakes of others, i hope he does well though i think he's in for a beating