Can Implants Become Infected Years After Surgery?

Yes. They can.
Although this is not a common occurrence, it is not unheard of. In theory, any presence of bacteria or fungus in your blood (IE bacteremia - as seen with blood poisoning [sepsis], severe mouth or urinary tract infection etc) can literally seed an implant.
We have known for years that people with irregular or noisy heart valves (those having murmurs) or those with artificial valves are at a higher risk of getting them infected with bacteria from elsewhere (known as bacterial endocarditis). Similar issues can be seen with artificial vascular conduits, knee and hip joints etc.
In the case of breast implants, it is not unheard of for breast implants to become hard (capsular contracture) years later, a few weeks after an infection. Rarer yet, we have all seen a few cases of implant infections as verified by positive cultures of the implant obtained at the time of their removal.
Personally, with breast implants in, whenever you have an infection or have your teeth cleaned, I would recommend you consider taking antibiotics to lower such risks.
I hope this was helpful.

Infections can develop in implants years after the procedure. But, I would have to say this is very rare.  Unfortunately there really is not anything you can do to completely prevent this from happening.