If you wait for a sim to reach their natural birthday, they will age up automatically. If you buy a birthday cake from Buy -> By Function -> Entertainment -> Parties, then any sim can blow out the candles at any time - it doesn't have to be their birthday! If you choose to have a sim blow out the candles, then they will skip the rest of their current age, and move on to the next one instantly. There's some variance, so sims can live a significant amount longer (and possibly shorter) than the numbers above. Note that these are not -exact- lifespans - sims don't automatically keel over and die when they reach 180 days on Epic lifespans.
Depending on traits, sims can live longer than the average life span (i.e. There is also an in-game 'No aging' setting - these are found in Options -> Game Options. You can change this setting at any point, and it will take immediate effect.
In TS3, you have the ability to control your sims' aging - or, more specifically, to set the length of their life to either Short, Medium, Normal, Long, or Epic.
