Life stage

A life stage is the age of a Sim. Sims do not age continuously, day by day, year by year, but all at once, "jumping" to the next stage in life.

The Sims
In The Sims there are only three ages: baby, child and adult.

Babies grow into children after 72 hours. Children do not grow up into adults, although the Makin' Magic expansion allows magical children to grow up by using the Age of Instant charm. There are third-party programs which can grow a child into an adult. There are also hacked objects which can allow a child to function as an adult - or vice versa.

The Sims 2
There are seven life stages in The Sims 2.
 * Baby: (3 days)
 * Toddler: (14)
 * Child: (24 days)
 * Teen: (up to 89 days) Note: Teens can grow up early in order to go to University.
 * Young adult: (varies; usually 90 days) University only.
 * Adult: (100days)
 * Elder: (varies300-8000 days) Sims who have higher aspiration levels when aging generally get more time, but there is a random element. Followed by death.

Note: The durations of life stages stated here are subject to two caveats. The first is that the aging off cheat suspends aging for all Sims. The second is that, from Teen onwards, Sims can use the Elixir of Life reward object to prolong life by 3 days (if successful) or shorten it by 3 days (if unsuccessful). Drinking from the cowplant can also prolong life for up to five days. Sims that are teen or older can become zombies or vampires, which also stops them from aging.

When a Sim is within one Sim day of transitioning from one age to another, it's their "Birthday", and they can then either wait for 6pm when they will automatically grow up, or players can trigger the age transition themselves with the "Grow Up" self-interaction, or the birthday cake. When using the cake, babies and toddlers depend on a teen, adult or elder to bring them to it. Furthermore babies don't have the "Grow Up" interaction - they always need the assistance of an older Sim to become a toddler, no matter what.

The Sims 3
In The Sims 3, babies and toddlers has been given 2 and 3 more days, but the others seem to decrease by 1 and 2. Also, elders will always live a minimum of 16 days. All Sims will now start from young adult if default.

There are seven life stages in The Sims 3.

The age duration for each setting (see Lifespan):

The Sims Medieval
Much like The Sims, there are only 4 life stages in The Sims Medieval: Baby, Child, Adult and Death. The player cannot create children or babies, only Hero Sims considering who can only be adults, however it's possible with "Age modifier" to induce the Hero Sim appear older, but techinically the Sims are still adults, female Sims with this appearance can still be impregnated. Babies will grow to children, but children won't grow anymore and they remain children forever. When Hero Sims die, their children won't occupy their profession, instead the player will have to create a new Hero Sim in CAS.