Based on sims 3 seasons where 4 weeks equalled 1 sim year. Therefore sims will age 1 year every 28 sim days. This means if you keep track you can have real ages for all your sims and know when their birthday is, e.g. if a sim is born on a Sunday then every 4th Sunday will be their birthday. Maybe a bit long for legacy play but useful for storytelling purposes.
Old lifespan:
Baby - 2
Toddler - 7
Child - 13
Teenager - 13
Young adult - 20
Adult - 20
Elder - 10
New Lifespan:
Baby - 28 (0 years old)
Toddler - 84 (1-3 years old)
Child - 252 (4-12 years old)
Teenager - 140 (13-17 years old)
Young adult - 336 (18-29 years old)
Adult - 840 (30-59 years old)
Elder - 588 (60-80 years old)
The above numbers are based on the lifespan being set to normal. Short will halve the above numbers and long will double them.