Is Prozac (fluoxetine) taken for years not good for you?

Not necessarily. If Prozac (fluoxetine) is helping you and you are not bothered by side effects (e.g. Sleepiness, jitteriness, lethargy, bleeding), then there is no problem with taking Prozac (fluoxetine) long-term. There is no evidence that taking Prozac (fluoxetine) long-term (i.e. Years) is harmful in any way.
Maybe. The side effects can sneak up on you. Gradual increase in weight. This is sometimes not suspected because it is attributed to other causes and does not show up after introduction - sometimes months to years later. Patients often find initial weight loss with Prozac (fluoxetine) finding it hard to believe it is responsible when they gain later on. Feeling more numb or flattening of emotions can occur. Apnea?
Pretty safe. Meds like Prozac (fluoxetine) are about as safe as any other medications, and have few if any long-term risks. There have been small studies suggesting risks-- I saw one suggesting slight risk of osteoporosis after decades of use- and they have some risk during pregnancy. But Prozac (fluoxetine) and other ssris have been prescribed in millions of people over decades-- and risks are small.