Here's our answer to the Fermi problem we posted last Friday . . .
The typical recommended daily allowance of iron is about 15 milligrams/day.
A 12 inch skillet weighs about 3 kilograms.
So a single skillet could provide a single person with 3000/.015=200,000 daily doses of iron before the pan is entirely consumed.
But a pan isn't very useful once enough of it is so worn away that it won't hold your eggs any more, so let's assume that you can only eat up about 1/5 of the pan before it's no good.
That means you can get your daily iron fix from a single skillet for 40,000 days, or 109 years if you use it every day.
There's a good chance, however, that the skillet is not just for you, but for a group of people like a family. The typical family has about 4 members. If they all get their daily iron from the same skillet, the pan would last about 109/4 = 27.25 years.
At least one cooking site claims that iron skillets will last a lifetime. If you define a lifetime as 75 years, our estimate suggests that they may be stretching the truth a bit. On the other hand, it's unlikely that anyone is going to use the same pan to cook family meals every day.
In other words, an iron skillet almost certainly will last a lifetime, but probably not much more.