The atoms in an elderly person and in a baby are the same age. In other words, the materials that only have one kind of atom in them. You identify elements by the number of protons. Taking one proton from gold gives platinum. Adding one proton gives mercury.
Platinum is more expensive per pound, so it is presumably more valuable.
The element is only determined by the number of protons. Oxygen has 8 protons. This is carbon. If it didn't the resultant element would still be carbon, it just be a different isotope since it would have a different weight. Protons contribute more to an atoms mass.