Are there markers in life? How does a man know if he is in his first or second half? Several authors have written on this topic (Levinson, Rohr, etc.). Clearly, everyone crosses over into life's second half differently, marked by biological, social, emotional and spiritual changes. These markers are guideposts (but not necesarily predictors), especially in a man's journey in life. (Additional reading on this topic are in the book Game Plan).
Be suspicious of the man who says he can do at 60 what he did at 30. He likely wasn't doing much at 30. Profound physical changes happen to us in life's second half. Just check TV for adds for "low-T," androgel, or Viagra.
What we need are images of life's second half that are free from the stereotypes. American society has a way of holding up icons of aging: Ringo Starr rocking and rolling in his 70s. My father-in-law is still farming in Kansas at 89. And many Baby Boomers are attempting to take their youth into old age.
The reality is there are some who live well into their 70s and 80s with the vibrancy they had in earlier years. And some come down with debilitating chronic illnesses in their 60s. The vast majority of men live with the aging bones, groans and hormones that are common and age-related.