Hello, due to chronic knee problem you have developed secondary osteoarthritis
which is the reason for your right knee pain
but the left one must be developing compensatory osteoarthritis due to increased demand on it as the right one is injured. Doctors don't consider knee replacement
at early age because you will have to go for revision surgery also at earlier age as there is a finite life of a implant and considering your age and activity it might be earlier then your elder counterparts. But knee replacement doesn't have a age criteria. It is always done for pain and patient discomfort. If you can't bear the pain you can opt for the surgery considering the pros and cons.