An antique theme revived in the late Middle Ages
illustrating the transience of human life
and thus a type of vanitas
. The number of ages varies (Shakespeare
in 'As You Like It
'), but three is perhaps the most frequently illustrated. The three ages are generally represented by two babies at play, a young man courting a young girl, and an old man occasionally counting his money, but more usually contemplating a skull
The maximum number of ages depicted is twelve, in which case an analogy with the months of the year is intended, although it's more usual, taking the course of a year as an analogy, to make the number four, thus establishing a symbolic link with the four seasons. When represented as four, the ages are childhood, youth, maturity and old age. In certain paintings the age of childhood is omitted and youth, maturity and old age are taken to symbolize past, present and future.