WAAAYYYY too old.
He would be even LESS likely to actively campaign than he did this last election cycle (where he spent fewer days in even the early states than the MOST lazy of the other candidates, Fred "Idowannacampaign" Thompson).
In addition, we would probably get yet another incompetent campaign team that would, once again, proceed to throw millions of dollars down the drain on useless and ineffective ads and personnel. (And if Ron's non-management technique is any indicator, his ACTUAL administration would, sad to say, be a disaster!)
We need someone who stands on Ron Paul's principles, but who actually knows HOW to campaign (and furthermore, who actually WANTS to win) -- and some experience in management or executive office wouldn't be a bad thing either (Johnson, Sanford, etc).