There are two questions to consider when you think about this fight and they are: Can Randy handle Tim and can Tim use his size to his advantage? First off, It has very little to do with age. The main problems for Randy are the facts that taking down Tim, a 265 lb 6'8" giant, is going to be difficult but also he will have to engage Tim which plays into Tim's other strengh which is his striking. Second, if Tim plans to fight defensively (as usual), he can wait and cherry-pick with his shots and in the unusual event that he does get taken down, Randy will have difficulty moving him around and Tim should be able to keep him in guard fairly easily. Randy moved down to LHW because he had trouble with big HW's. Don't get me wrong, I love Couture and respect more than any other fighter, it just doesn't seem logical that he will win.
Sorry Randy, and I'm still pulling for you.