The older contestants always come in with a disadvantage, if they can't prove right away they can cut it in challenges they become easy targets for the "keep the tribe strong" argument. But Mark seems to be in good shape, and he also served during 9/11 so I have no doubt he is prepared for anything Burnette and Co. throw at him.
I think how Mark does will depend on if he allies with the right side early on. If he picks good alliances he will likely go far, if he makes a bad alliance first off he will be a candidate to leave early.
He talks about being an honest person in his CBS bio. If he decides he is going to play the game "honestly" he will not win. One thing I have learned from Survivor is people who try to play "honestly" either go home early on, or talk about how honest they are while not doing what they preach and end up resented and don't get the votes if they do make it that far.
He seems cut from the same mold as some of the older winners of past seasons however. So assuming that he makes some good decisions early on I think he could go far. But he has a lot of things in his interviews that has me concerned he won't end up an early target.
Here is Mark's interview on CBS's YouTube Channel.