I'm only 31 and in the same boat (size A, breastfed my kids, etc). My favorite teacher died this summer at the age of 53 after being diagnosed two years ago with breast cancer. If you have breast implants, it can be more difficult to detect breast cancer. The implant can obstruct the view and delay treatment for the cancer, which leads to a 26% higher rate of the cancer spreading than in someone that didn't have implants.
With that said, I'm going to consider a breast lift. There isn't much to lift, but I'm on the fence about implants.