Age doesn't bother me that much- just his heavy load as a Steeler. I think the biggest concern with the year off is degeneration of football muscle. Some of that can be bought back with hard work, but the reality of it is that most of these guys have been using their body for this sport their entire adult life. All the little muscles and tendons are used to this specific job and this specific workload. Now, after a year of atrophy (especially if he was really up to 260, like the rumors say) and you have to wonder about the ACL's and the Achillies' and the Hamstrings. It's just something to worry about and the problem is that it's not really testable... (and the flip side could be that he comes back better than ever and well rested, who knows.)
Also an important thing to think about is that he's been off NFL radar for a year... who knows what injuries (a torn pec while lifting? Strained hamstring while running?) he might have had- or the other side of that - drugs and alcohol. It's not a deal breaker per se, just makes me hesitant before overpaying.