1 Few static lines - Under 25
If a person is below 25 years old he will usually have very few or non existent static lines. Static lines are the lines that are always visible on the face even when the person is silent; for example, smile lines and forehead lines.
2 Adult and youthful - 20 -25
When a person looks a little more like an adult but still retains his youthful look then he can be anywhere from 20 to 25.
3 Facial lines start to appear - 25-35
At around 25 some static facial lines can appear such as forehead lines, smile lines or lines around the eyes.
4 Few grey hairs - 30
At around 30 few grey hairs can start to show up. Those hairs are usually very few but in some cases people develop lots of them in their thirties or even before that.
5 Less defined jaw line - 35-45
At around the age of 35 the jaw line can become less defined.
6 Lots of grey hair - 30 to 45
If a person has lots of grey hair but his hair is still not completely white then he might be anywhere between 30 to 45. (See Why do we develop grey or white hair?)
7 Sagging upper lid - around 40
At around the age of 40 the upper lid can start to sag or fall down a bit.
8 Laxity of the skin - around 40
At around 40 the skin can become more lax as it loses its elasticity. This laxity also usually happens in the neck as well.
9 Very clear lines - 45-55
At around the age of 45 aging becomes very evident and lines appear in so many places in a clear form.
10 Intense facial lines + laxity - 55 to 65
When a person reaches 55 his skin laxity increases and his facial lines and wrinkles become very obvious. (See How to slow down the aging process?)