Absolutely not. There’s more 5+ year old does in the population on most properties simply as a result of harvest strategies by hunters. VERY few bucks live to be 5+ due to hunting related and natural mortality. 5 year old bucks are no harder to kill than 5 year old does. They just simply don’t exist in a lot of places.
Lota truth here, there's way fewer 5YO and older bucks. That aside , I'd say the buck MAY be a little harder to kill only because I think those older bucks are like grumpy old men and are more reclusive than does. Even if there's a difference , don't know how you'd prove it.