Is Hillary's age going to be an issue? I don't think it should/will be but some people will try to make it an issue.
No, and I really doubt anyone will seriously try to make an issue of it. There are plenty of legitimate things to attack (hypocrisy on wealth and taxes, exagerations and outright falsehoods, her war against Bill's Bimbos, lack of experience, incompetence, just generally being a lousy candidate, etc.) without engendering sympathy with ageism.