Yes, not so much from a succession standpoint, but from a skill/experience value-add.
We live in a time where medical science and health care advancements removes a lot of the issues we saw where VPs filled in for dying presidents. And by "a lot" it's happened, what, 3 times? We won't see deaths from pneumonia (Harrison), eating fruit and milk and developing "illness" (Taylor), even the heart attacks and cerebral hemorrhages we saw strike down Harding and Roosevelt are somewhat mitigated in today's day and age with general awareness, preventive care, and much better reactive medicine.
All other instances of the VP stepping in had to do with assassination and resignation.
So rather than worry about a president being over 70, I worry more about whether the VP has a solid track record and expertise that compliments the President's, or adds a level of knowledge and skill that the President may not necessarily have.
Biden, for example, didn't add much in my mind to what Obama brought to the table, but didn't detract so didn't give a hoot. Cheney clearly did add value and skill that GWB sorely lacked so could see why him being a VP provided a good underlying additional skill set. I really thought McCain was a really qualified candidate but Palin with her faltering record as Alaskan governor, inexperience at a national/international stage, and often coming across as unpolished, almost detracted from McCain's strengths.