Sentence:  By then one <WSD>begins</WSD> to notice the middle-age spread ; the gray hairs , the eyeglasses , bodies that are too thin or too heavy ; the fading signs of old beauty ; the athlete of by-gone years who wears a size 46 suit and puffs when he has finished a sentence of any length ; then , it is time to break it up and move on . 
Meaning of the word marked with <WSD> tags:  take the first step or steps in carrying out an action