Actually you don't have to worry about the Sims aging, as long as you type in the cheat Aging off (I had it right after all :O) then your Sims can stay the same age. The only problem with this as far as I can see, is that you can't have some Sims age and not others- for example you can't have two adult Sims have a kid, then have that kid grow up while the adults stay adults.

But it's great fun! How are your Sims going?