What indicate the start of old age?

you can tell it by the health

I have come to believe that old age is a state of mind rather than the physical attributes of aging. I had grandfathers who lived everyday of their lives well into their 80's, and both had the attitude of someone who wasn't ready to look at old age or aging as a negative. I think it starts at 25 for some and 95 for others, based on the perspective that they hold

Heart makes you realize that you are getting old , If your heart is young than you can not be old . It's all depend on thinking that you would like to go fir outing or sit like old man and read newspaper .

I don't think so. Now-a-days even youngsters also facing the grey hair problems. I think face can reveal the aging process.

I think the start of old age begins when you start walking slow and slumped over. That sounds kinda rude, but I don't mean it that way.