1. The size and angularity of the neck and shoulders: Babies start out with thick necks, but then by the time we’re 5 or 6 our necks seem to look pretty skinny (at least I’ve found it seems to look that way in drawings). Our shoulders, obviously, start out small and get broader and broader as we get older (this is more apparent in men than in women, of course). Also I made a conscious effort to make his shoulders start out rounded and get more angular as he ages. If I’d kept going, drawing this guy into old age, I would have made the shoulders start to shrink (and get more rounded again) as he aged.
2. The relation of the mouth to the chin: I simply made the mouth get further away from the chin as he ages, to give a feeling of a jaw that develops as he gets older. Also I made the jawline stronger and more angular with each successive age.
3. The amount of upturn in the nose: I made it turned up more in the younger drawings, and made it less so over time.
4. The size of the forehead: We have a bigger forehead when we’re young, and it diminishes proportionally over time.
5. The chubbiness of the cheeks: most of us have less fat in our cheeks as we age.