If you think you are over the hill, then you are. It doesn't have that much to do with age.

Oregon Mouse of this forum is in her 70's and still going strong; I'm in my 70's and still going; I think OM passed me on the trail once. I met two 70-somethings and one 80-year-old on the JMT this past summer.

If you don't have any major health limitations, then being "over the hill" is a choice, not a condition.
May I walk in beauty.