Marian, this is interesting question, but I don't know the answer. Age of other Sims is questionable with aging bug, and the fact that (at least some) Sims that are not living in a house in a town are not really aging (and that is how some of the original Sims can live as long as several generations of other Sims).
Still, I believe that if your Sim friend eats ambrosia and his/her age reset, then other ways of extending their lives should work too, including life fruit in nectar. I'm sorry for not knowing more, and I hope someone else will provide us with more accurate answer.