I was told by my doctor that they prefer not to do knee replacements on people under 55 years old. His explanation was that knee replacements are good for 15 years and they don't like doing multiple knee replacements on an individual. I guess they settled on 55 because the life expectancy of an average American is 70 to 73 years, so you can do the math there. My doctor told me only in extreme situations when they do a knee replacement on a younger person. I do have a former coworker who had knee replacement on both knees at 42 years old. So depending on your situation, you might be able to still have the knee replacement.