Buttock implants longevity: what happens to your implants when you get older?

Say you get butt implants in your 20s (me) - what happens to them when you are 50, 60? You lose muscle as you get older right so won't they sag? Just trying to figure out what long term situation is with them since they are kinda new. What about how older people get sciatica? And hip implants? How will the butt implants affect all these things? Will they make them worse / cause complications? Not really worried, more wondering