When is a person considered to be of "middle age"? From what age to what age?

Probably depends on your mental feeling in addition to age. I would consider 45-60 middle aged. I am a lot older than 60 but keep a good mental outlook, exercise a lot and keep busy. I don't consider myself aged.

I am 64 and I think I'm getting close to middle age, though the body begs to differ, as do my kids and grand kids, but what do they know! What is your definition of middle age mean?