For me, it depends on the Sim and what their initial career is. For my athletes I normally have them quit once they age up into an adult or not long after and choose something else that interests them. Other times I've had my Sim just stay in their career until they are an elder then have them retire to enjoy the fruits of their work.
As for family, I tend to let the Sim decide if they really want to get married or have children (sometimes there are oopsie babies becaue of MCC and autonomous Woohoo).
