Saw facebook photo of old woman in bikini who had breast implants. They were really low, so is that what happens?

Not Necessarily. As you can imagine, every woman “ages” differently when it comes to the appearance of their breasts. Much will depend on factors such as genetics, history of pregnancies, history of weight gain/loss etc. Every patient undergoing breast augmentation surgery should know that additional breast surgery will likely be necessary in their lifetimes.
I think I saw same. I think that picture would scar anybody. There are several issues here. Iris a large implant in an especially thin individual. Modest implants in normal body weight individuals may look considerably more natural. Many changes that occur with aging may effect the appearance of the implants and this includes implant size, volume of natural tissue, over/under position, contracture, sagging, lax skin, .
Likely. Breasts normally descend with time even without inlmplants. Implants can make this process occur more quickly and more dramatically.
Breast Implant Age. Depending on the size of the implants and how well your skin holds up or stretches as you age, they can look pretty good after several decades or stretch out somewhat. Your surgeon can discuss the relative risk of this happening in your case.