Knee Replacement at 33 years old??

I have had 15+ surgeries on my left knee that has stemmed from a birth defect where my left knee was anatomically deformed. In those 15 surgeries several doctors have tried to make sense out of what they say looks like a "ball of yarn". They also said I have knees of a 80 yr old woman.  Through the years I have had 2 ACL repairs, countless scopes, patellar realignmnet and a tibial tubricaI transfer.  I am now 33 years old. I have no ACL, no PCL, zero cartiledge and 80% arthritis in my left knee and 70% in my right. I am in extreme pain, I walk only on crutches and am now looking at motorized wheel chairs.  This is not acceptable to me, as I have NO quality of life.  My surgeon says that he will not do a knee replacement until I am in my late 30's.  WHY?????????????  Is there any alternative to this problem beside a knee replacement between now and 4 or 5 years until THEY decide THEY will do it? Please help!!  Thank you!