I play with aging off because I want to really spend time with my characters. Because I have Seasons, I try to semi-consciously follow a "real" timeline... manually aging characters when a certain number of years have passed (assuming Teen is roughly 14-17, Young Adult is 18-29, Adult is 30 - mid 60s and Elder is 65+ ... Toddlers and Children I tend to age up a little faster). Of course, I change up the length of a season as it suits me so some "years" are four sim-weeks long while others are much, much longer.
Pregnancy I want to set to three seasons... though after leaving poor Morgan pregnant for nine full Sims-weeks, I've decided to shorten seasons during any actively played pregnancy to one Sim-week per season.