Yes kicking sims out is your easiest option. The normal way (story progression) is that other households progress through their lives while you play with one family - it is possible to undo that setting and therefore control all households but it comes with it's own problems.
You can see the lifespan of a sim in the first tab (personal info I think) and hover your mouse over the little bar and it will tell you how many sim days are left before they age up. The ages are: Baby, Toddler, Child, Teenager, Young Adult, Adult, Elder. How many days for each can be adjusted in the options.